I'll add a sixth or tenth "GW has not changed", but also add that "players' rosters change". If you see more zetaed/omegaed squads, it's mainly because your top 5 has become stronger, but also because all the players, old or new, pay more attention on omegas and zetas. When I look on the Arena competitors of my younger guildmates or mentees, I see squads that I didn't face when I was at the same point ; but my mates also field far smarter teams than I could back in the days.
People check the forum, check reddit, get advice from their guildmates through chat apps, so that their team comps are better thought out than 18 months ago, or even 12. At the same power, a Wiggdo/JKA/STH team will be much stronger than a Chewie/JC/Talia/TuskenRaider/Greedo.
Also, more and more players manage to get a lot of zetas by now, so that they can have their sixth, seventh or tenth toon with a zeta - so not everyone has zetas only on their top squad. This brings more variety on the zetas we may face. And you should follow the movement if you want to be competitive.
It's the same as what happened last year when Wedge became farmable, or early this year when Emperor's Demise came back - while those characters were known to be powerful and game-changer at the time of their introduction, few players could field them. But as soon as most players got their hands on them, they became ubiquitous, and GW looks harder and "changed" - but it's not, it's just that knowledge spreads, best practices are discovered and learned. The same happens now with Nihilus, GK, Chaze, etc - if you did not anticipate their ubiquitousness (must have been pretty short-sighted to miss that) and prepare counter-teams for GW (if not Arena), it's your problem.
As has been said above, GW is not meant to be beaten on auto everyday, it's meant to test the mettle of your roster, and your skill at picking the right squad to beat any given node (and it has been said so numerous times by devs). If you manage to beat it with one squad on auto, fine for you, enjoy - it won't last ! If you don't understand that, it's not the fault of the dev's.
tl/dr: don't expect the other players won't improve their squads ; improve your roster to deal with them