And if the great classical composers were around today they would be using Keyboards. Check out Jordan Rudess and Keith Emerson. Both classically trained and they use keyboards.
But there are literally thousands of musicians that are "classically trained" It doesn't mean Jack sh*t. Besides Maksim isn't a great composer is he? I mean, you'd be hard-pressed to seriously compare the best pianists you can find today with great composers [barring that the 2 sets overlap and they are often the same] - that would be just laughable. You may as well say "Beethoven would compose using a biro and an Ikea desk". Who cares?
Worse, when they sell that idea hoping rock / pop audiences will think it does.
The names you list here, [and TBH the other thousands of classically trained people in Jazz, pop and rock in production as well as performance] are conceptually different from the Maksim's / Klass / Mae / G4 et al...because the latter are pretending to be classical musicians sometimes even playing classical rep whereas the former generally aren't.
The former deserve some contempt only because they [or at least their management] are trying to sell themselves on some classical credentials, which isn't quite as bad as trying to pretend they are actually classical musicians.
Bear in mind, in a poll of best guitarists, Jimmy Page ranks as high as people that can play the guitar much better than he can. It's not difficult to look good in the rock world if you've got some chops, but it only takes you so far.
See the difference? If you want to be a lawyer, do the training and be a lawyer. But, if you get 'lawyer training' and turn up to court dressed as a clown and lose your case then you should probably expect to be treated like a clown. Lastly, getting a job at McDonalds and telling everyone that you've got a law degree, fine, but don't expect any of the others to be impressed - you'll only be as good as you are at clowning. Which isn't based on law. Is that too idiosyncratic? What I'm saying is that Jordass et al needs to be good at Rock ['McDonalds"] irrespective of how good at classical ["law degree"] they might be ergo Maksim's failure imo.
What's a chocolate milk shake in this analogy? What kind of fast food are Jazz and Rap? I don't know - I didn't think it through that far. Perhaps one of those jacket potato places with the real oven rather than a microwave?
Considered as an artist that's playing rock / pop that takes influence from classical [and other genres] I still think he falls into the Mae / Klass school of failing miserably to do it well. e.g I can't see his next album competing with Zepp, Tull, Hendrix, Zappa, Beefheart, Muse, Vai, Floyd and so on...Rock isn't about chops, but there's no shortage of chops anyway as you note.