At least the non-earth modes made sense, as it was set in the "far" future of 2005, so you could imagine the alt modes being cybertronian or futuristic earth vehicles. But those S2 guys... they showed up from nowhere, without explanation, and completely replaced the ark crew.
At least the movie gave an in-story reason for replacing the previous characters, i.e. they got smoked, even if it was a shitty sales stunt. S2 didn't bother. We went from Jazz and Mirage doing cool stuff one episode to "Whiz, bang, pow" Warpath, psychopathic Red Alert, traitorous insubordinate british-prick Hoist, insufferable Powerglide, Hee-Haw Inferno, and hippie-dippy Beachcomber. Those assholes just took over the show without warning, like they thought we were too stupid to notice. They're the "Coy and Vance" of Transformers.