Your quote is from someone trying to justify silly contracts offered by Barcelona. Just to show how dumb that quote is, if your point was actually true, the gap between players wages within Barcelona wouldn't be that big that's what a wage structure will do for players of similar level yet. For example you wouldn't have Dembélé earning signficantly more than Coutinho even though the latter joined the club a few months later and being a more established player. You wouldn't have Alba earning less than Dembélé or Sergi Roberto. You wouldn't have Arthur earning 4 times less than De Jong when he joined Barcelona even though both deals happened after Messi's contracts.
It's not even debateable that wage structures aren't actually a thing, it's a nice idea that may have fooled you but you just have to look at Barcelona's contract after Messi extension in 2017 to realize that the quote is completely bogus, there is no logic in the contracts given by Barcelona, there is no structure or discipline.
The quote is someone with actual knowledge of Barcelona's contract negotiations. That's something that you don't possess. Someone who actually knows what was going on with Barcelona's contract demands and what benchmarks were being provided. All you can provide is incorrect contract figures trying to prove a futile point and irrelevant lines like "the quote is dumb".
Dembele earns significantly more than Coutinho? Where's your source for this?
Closest thing to verifiable info was the Football Leaks which had Dembele at -
"The 20-year-old Frenchman is to receive twelve million euros of FC Barcelona at the club, at best including bonus payments of more than 20 million." - Source, Spiegel/Football Leaks
This is GROSS. Gross €12m rising to €20m gross with bonuses.
whilst Coutinho's NET is at around €12-14m with gross around €24-27m (unsure on bonuses, not included I believe) -
"There was, in fact, a 20 page agreement between Coutinho and Barcelona on August 31 and the Brazilian would have earned 115m euros over five years with his agent pocketing 10m if the up-front transfer fee was 100m." (gross)
AND
"The club will look to sell him and use the money they receive to reinvest into the squad, while an exit would also free up 13.5 million euros from the wage bill." (net)
AND
"According to BILD. Buy option is 120M and Bayern will take over his 13M (net) salary" which works out to €26m gross salary
Sources - Marca, Bild and Spiegel/Football Leaks
So, the idea that Dembele earns "significantly more than Coutinho" is incorrect. Won't even bother checking other contract figures you've cited because you couldn't even get the first two correct.
And you talk of Barcelona's "wage structure". Yes, I agree, my exact point, they don't have one. It was shattered by Messi's obscene contract, distorted by the other obscene contracts and then financial incompetency piled in on top of it.
With regards to "wage structures" not existing. I find that laughable. I'll leave you with a quote from Bayern regarding Kroos' contract -
Beckenbauer said: "You have to make a decision as a club when someone's demands are going through the roof. There is not a single player who's worth changing your entire wage structure for. Nobody's indispensable. If the player wants to stay at Bayern, I can only advise him not to overplay his hand."
Presume Bayern let Kroos go for free for a "wage structure" that doesn't even exist. Jesus H Christ.