Are today's top correspondence chess players stronger than those from 5 years ago? On the one hand today's chess engines will stomp those from five years ago no problem, not to mention hardware improves; on the other hand, correspondence chess players emphasize that one can't just rely on the engine to play:

DN: Every how often do you have to change your machine?
WM: I've never changed my 'machine'. If we're talking about my computer for chess analysis, I'm using the same computer I've had since 2008. Modern correspondence chess isn't all about CPU power (although that obviously helps), but more about how you prepare each move and how you work with the engine in tandem with your own ideas. You can get lazy and buy a powerful computer, and probably get to a fairly decent rating on ICCF just parroting the engine, but that's not going to take you to the top ...

Are today's top correspondence chess players able to reliably beat those from five years ago?
Related: Are contemporary chess players now stronger than players in the 90's or 80's?
Yes, mainly due to more advanced theory that wasn't known five (or more) years ago.

Also, while top Correspondence players do indeed combine engines with their own ideas, having an Engine that is a few hundred rating points higher is a definite factor. I find it hard to believe the person you quoted uses the same engine he has for 10 years. If he means the same computer though (so running the most recent Stockfish/Komodo/Houdini on an old computer), that sounds more understandable. In this case he's only sacrificing the amount of speed that a PC 10 years older gives up compared to PCs now.