Essentially Mbappe would be the best player in Premier League history without even truly starting his career because he was a key part of a France world cup team that won a world cup and has been doing well in a weak french league.
Were Pogba/ Kante better players than Roy Keane or Scholes or Gerrard.
No, yet many will say they achieved far more at national team level than any of them.
If Keane, Scholes or Gerrard are better players, is it because they won the Champions League or were we able to watch them each week, allowing us to use their performance each season to decide how good they were.
The obvious answer is Henry, its not even close. For a two year period, he was the best player in the world, prior to Ronaldinho taking the crown. He's considered the Premier League's greatest player, not just because of his goals, but because of his all around play which made him consistently unstoppable. Arsenal were not a good enough team to win or have much impact in the Champions League, so his impace was minimal. However, when they did go far, he dragged them to the Champions League final, a team on its last legs. When he did win the Champions League with Barcelona, he played a similar role as Mbappe has been playing for PSG. In that 08/09 campaign, where Henry was clearly in decline, he scored 6 goals. Mbappe has had the Champions League benefit of playing with a PSG team that had better players than him for much of his time there. He has only ever achieved 6 goals once. Despite Arsenal's level, Henry had dominant Champion's league games for Arsenal, like the Inter game in 2004, Roma in 2003, Real Madrid in 2006 and Juventus in 2006. Just to show how overrated the idea of scoring in the UCL is, Henry at Monaco got 7 goals in 1998 for a Monaco side that made the semi-final. Was that version of Henry better than the one at Arsenal? By this notion, Bale is the greatest player Britain has ever had and Neymar must be far superior to R9 or Rivaldo or for world cup's I'm sure Miroslav Klose must be a better player than Ruud Van Nistelrooy.
Now for what is actually important. Henry played had 7 great seasons at Arsenal, with his last one being injury ravaged. For 5 of those season, he was out of this world. For 2 of those seasons, he was arguably the best player in the world, in that window of time, he managed to establish himself as the greatest player in one of the most dominant leagues in the world. Mbappe's club career has come nowhere near that.
On actual play, Henry was better technically. He had the touch and balance of Pogba, he was a massive creative threat, plus he was a better finisher. He had similar speed, with Mbappe being sharper and more explosive. Mbappe actually looks like a mixture of R9 (when on the flanks) and Jean Pierre Papin. He hasn't been a better player than Neymar until now, and Henry was as good as or better than Neymar was.
This discussion is like asking people in 2001 if Micheal Owen was a better player than Alan Shearer because he had won a Ballon D'or and achieved more in Europe. Owen still had a bit to go to achieve that, even though his trajectory suggested that he would be. He never actually ended up getting to that level, both as a player and in achievement. That's how I feel about this discussion. Mbappe given time will most likely be considered better than Henry; his current trajectory suggests that he could end up being a top 10 player, but trajectory doesn't equate to achievement. One year ago, Mbappe was being insulted by everyone after France's Euro performance. Now he's being praised to this level and we aren't even in the Quarters yet. France could win a World cup with him getting injured, would that change everything? What if France lose to England?
The debate feels slightly insulting really. Throwing a great players career on the slightest whim of someone being good. Haaland and Mbappe can't just be very good, no, we need to ask whether they can match Messi or Ronaldo despite thousands of striker's who have achieved more and have shown levels of consistency that they haven't yet or may never end up achieving.