This migh be a bit long so i'll divide it up in different parts
On Messi Goat level :
Ever since he moved to the right, he was still the best player in the world for most time but if we talk strictly GOAT level he was not. Disagreed on 10/11 point of him turning into a lazy git, its more from around 2013(roughly) as you said.
Let's agree to disagree. For me, Messi was the best player in the world for a while after he was already past his physical peak, but I certainly wouldn’t say that his later seasons were GOAT-like. He barely contributed off the ball and his acceleration wasn’t quite as sharp. As Sjor said, that’s disrespectful to Messi himself and to his best seasons, which very well may be the highest individual level that any football has ever reached (personally I’d put his peak second after peak Maradona, but the difference is marginal).
I don't understand the focus on the defensive contribution, ever since Guardiola got in charge he was always mediocre in that aspect of he game and abysmal since 2013, It cannot be used as an argument to say that his level dropped off. He averaged 0.9 Tackles+Interceptions in 2015 and 0.7 per game in the 2016-2019 seasons, both figures are ridiculously low. Surely if we want to talk about a supposed decline, it is not the aspect of the game where he is the least impactful that should be brought up.
He lost some lace for sure, be he also improved other aspects of his game to fill his new role. Mainly shooting from distance and free kicks. His goalscoring total is a bit less impressive from those years but that's because he plays further away from the goal, not that he can't play up front anymore, but Iniesta getting older and leaving the club left a huge creativity void in the midfield that he had to fill.
Again, his performances against Real in 2017, Juventus in 2017-18, Tottenham, Man Utd and Liverpool in 2018-19 were some of the best in his carreer. I can't share links with you but i invite you to check them up and tell me how that version of Messi is inferior to his 2015 self.
As i said, one could consider 2015 version of him as his peak for sure, but saying it's the last time he played at GOAT level is incomprehensible for me because it's absurdly high standards otherwise. If 2015 is the threshold for playing at a GOAT level, then no other player in history had a GOAT season. (We can't say about Pelé because we lack footage of specific seasons).
About winning bias :
You’ll never get a fair and objective comparison as every player’s situation is different. Would Messi win (possibly a couple) World Cups with that Brazilian side? Truth is, we’ll never know, but it’s almost impossible to think that he wouldn’t. But you can’t count in the performances that we can only imagine in comparison to the real performances of, say, Pelé or Maradona, and the truth of the matter is that he hasn’t produced anything close to their 1958/1970/1986 campaigns. And you can’t use club performances in discussion about international ones.
It's not because we cannot get an objective comparison for every player that we shouldn't try to do it when we have the ability to do so. And in the case of Messi and Pelé we do have a fair amount of elements to have this comparison.
I do not count performance that didn't happen, but i certainly take into account flukes, and that when you deal with small sample sizes the results are going to be inevitably skewed, and those things have to be taken into account. If youre familiar with Basketball you'd know that Lebron James in 2009 had the best post season of all time in 2009, better than anything Jordan ever produced, yet it cannot be used as an argument to prove his superiority to Jordan because we do know that it is not representative to his average level but more the result of an insane hot streak. It is just an exemple of how small sample sizes can skew things up. Now you can imagine how a 7 game tournament that takes place every four years is prone to these kind of discreapancies. Therefore Judging Messi on his WC is to me a flawed method, especially when we have a bunch of other instances where we know he performed to a level similar or better to the other All time greats.
Why ignore it and not take it into account ? As in Sjor Bepo's words, why is it always him lacking something, never what others lack compared to him.
You say it yourself, how fair is it to compare Messi and Maradona club performance when the former had a much better supporting cast ? Why does this logic not apply to Messi and Pele International tournaments then considering how superior the brazillian supporting cast was to Argentina's ? You are able to take into account nuances when comparing Messi and Maradona club performances, then there is no reason to not do the same with Messi and Pele.
On Messi WC 2014 performance :
Still, I find those stat comparisons pointless — I don’t need to see dribble stats as they won’t change my perception of how much better Maradona-86 was compared to Messi-14 (or any international version). And Maradona’s team was not all that — he didn’t win it single-handedly, of course, but he came as close as you theoretically can.
Should we rate players by their WC performances? Not exclusively. But then how fair is it to Maradona, for example, that Messi played in arguably the greatest ever club team? Et cetera. There’s always going to be nuances and details, hence why I usually think about them in tiers and not in strict numbers.
For example, I think that Pelé is the greatest, Maradona is the best (in terms of his peak ability), but then I’d probably put Messi second in both categories ahead of Maradona for greatness & Pelé for ability.
It’s all about fine margins anyway without any real chance to eliminate all of the variables.
I think
@Šjor Bepo said it all in his post. As i pointed out in my precedent post Argentina 2014 was arguably even less creative offensively than in 1986 as Burruchaga was a decent creator and Valdano was clinical, while Messi had no one to assist him and Higuain was botching opportunities left and right.
So in 2014 he was not bad, but he was not put in situations to succeed by his teammates, if you only receive the ball in the midfield, even if you dribble 2 players you are still 30 meters away from the goal and unable to make an impact. This is why the number of dribbles, forward passes and carries is important, because it shows that the player had the ability to make the difference, but he was not put in condition to do so. And despite all that it's still crazy to say that Argentina could have walked away with the trophy with just a little bit of luck. I really suggest reading the article "If we knew what we know" that compare's Messi and Maradona it's really a great read.
At the end of the day i don't think it is particularly wrong to rate Pele higher than Messi, because as you said it's all about fine margins at this point, but i feel that some arguments who are used against Messi are unfair and that he gets more criticisms than he deserves just for that missing WC win, because if Higuain had smashed one of his chances in the back of the net, we wouldn't be having this discussion, because there would be literally no single stain on Messi GOAT case. . Letting such a volatile variable influence our judgement and perception is frustrating to me.
P-S :
@Šjor Bepo Great post, just a little precision, the game against Belgium was in the quarter finals, and the game against the Netherlands was in the semi final.