He has to now be consisered the most effective player in the league. What amazes me most about him is his game intelligence and how he can be so decisive at 22 years old. This is even more surprising when you consider he wasn't a guy playing mens football from 16-19 like a Bellingham, Rooney, Mbappe etc.
It isn't an accounting trick as that has already been dealt with by UEFA. As for the contract, the outline above about how it allows him job security and wage increases makes sense. However, I imagine the part Chelsea get out of it is assurance he isn't going anywhere and this is pretty much as close to the US system in football where the teams have a lot more power.
Additionally, if anyone has seen Cole Palmer do an interview, the likelihood of him considering moving to Spain or Germany seems a bit remote.