I don't understand what is so confusing. The wage in itself is not a problem the problem is:
A) You're giving 400K to a player in his 30s what if his form falls off a cliff a year (for example) into his new contract?
B) The likes of VVD and Allison may ask for parity and are they not just as important as Salah? Any new player you sign may ask for parity.
You're making a rod for your own back and opening Pandora's box and once opened you won't be able to close it again.
B.) The argument for this would land better if Mane and Salah hadn't already just asked for more money than anyone else currently at LFC. What is to stop VVD, eventually Diaz, Trent and Allison doing the same in a yr or 2. If they did we would have let Salah and Mane go for potentially no good reason, if this was one the main reasons.
Sure new players may ask for parity with Mane's potential new LFC deal, but we generally sign younger players like Nunez/jota/diaz who are unlikely, we rarely go for Thiago types transfers.
So I don't think these are the reasons we let Mane and might let Salah go. I think we may a tactical and squad morale based decision. Nunez was going to play and Firmino is more likely to accept being on the bench than Mane. For all the hype about a 5 great forwards last yr, Klopp had a clear preference for this 1st team forwards and their will be a clear preference next season, and it may not have included Mane, now that Nunez has joined