I think you've missed the point completely. We're not talking about specific amounts, we're talking about relative amounts with respect to the wages being seen to be paid by the club. The 'wage landscape' if you like.
Whatever Jota's agent asked for when he joined, he would have asked for a different amount if the wage landscape at the club had been different. It's the same basis by which a player going from a PL club to a lower league club has to react to the very different wage landscape by expecting and asking for less, and how a player going from a lower league club to a PL club will automatically start negotiations at a much higher level.
No - you've missed the point by completely misunderstanding the role a "wage structure" has on a new player into the team, and what kind of wage they can negotiate - almost NONE. You are pretending that if Salah was on, say 250k, instead of 200k, that Jota's demand would have been more - that is simply not the case, or if it were the club would have laughed at his agent pretending his client deserves more just because 1 player is paid more.
There is, however, plenty of evidence that the pay of a new player, mostly, is dependant on 2 things - the size of the transfer fee (so the cheaper, the easier it is to get a higher wage) and their current wage (so if they are on a higher wage, it will be difficult to sign them on less); turnover/revenue of the club also can count. Jota was on 40k at Wolves - he came to us on 80k. So you might say "oh that's a big pay rise" and it was - but his fee was less than other (often bigger named players) were pulling in, so we could afford to add say 20k to what we would ordinarily pay (20k a week, across 5 years, is only 5m), and it's still less than comparable players in our squad and similar clubs'. Milner on the other hand was on closer to 80k at City, but when we signed him we gave him a much larger raise up to 140k - because his transfer was absolutely free, despite being at a time when wages were about 25% less than when we bought Jota, and in a position where you don't earn as much in general (MF vs Attack). If we had to buy him for the market value of about 20m, then he'd havbe probably been offered (and been happy with) closer to 100k
Let's be clear here - the agent's main pay day is NOT the contract renogotiation but at the point of transfer - so using the "greedy agent" logic, then they want a new player to arrive for more money in the form of the fee, and less wages (especially as then when they do re-negotiate 2-3 years down the line, the increase they get their client is larger, so more money again for them). They would get far more money if they signed shorter 3-4 year contracts, and then moved their client after every 2, then do what the likes of Salah wants and sign a (bigger) contract and stay another 3-5 years (and possibly get another contract at that point).