I don’t know what you two are talking about. The various series were mostly hit or miss but it hasn’t been a steady decline.
G1: First season is actually pretty damn good considering the time and age of the series. Which was unfortunate given how the second season was a giant toy commercial. Haven’t seen the Third, Fourth seasons, or the movie yet.
Beast Wars: Do I really need to make a case for this? Still the best damn series in Transformer history by miles and one of the best fricken shows of the 90’s.
Beast Machines: Eh. Slow start and kinda got silly near the end but wasn’t too bad in retrospective. It’s biggest mistake was succeeding BW.
Robots in Disguise: Pretty damn anime and got completely ridiculous at the end when it was like 30-40 Autobots, most of which were sporting powerups and mid season upgrades, versus 6 Decepticons, and with only 2 Predicons remaining (and that includes Megatron), neither of which were on the same side. And the Autobots were getting their asses kicked like a bunch of chumps.
Armada: Now this one was alright. The Minicons turned out to be one of the better Transformer gimmicks plus a morally conflicted Starscream, Unicron’s involvement in the end really, and a general balance in power between Autobots and Decepticons helped keep the series above average.
Energon: The less said the better.
Cybertron: Just another blatant toy commercial.
Animated: The latest series. Was pretty damn awesome, if for no other reason, than having The Tick personified as Sentinel Prime and something resembling something like an overall plot arc. Probably rate it second after BW.
Bayformers: First one was surprisingly watchable. Second one was unsurprisingly not.
UK Gen2/Japanaformers: Whole 'nother ball of wax, those are.