Nah I wouldn't say stop playing all TW games. I'd just say wait for community mods, which will make Rome 2 much better over time, mark my words. The TW community has never failed to come up with at the very least one or two "major" mods that ultimately make every single one of the TW games better than their vanilla counterpart. You don't even need complete conversions, or gigantic mods like Darth Mod, something more "humble" still usually does it.
To be completely honest of all the TW games I own I haven't bothered to play any of them under their vanilla state, in years. And to be frank I don't remember a single one of them being "very good" at release day, they all needed at least a major patch before being "playable enough". And then the community kicks in (usually it really kicks in after the second patch comes in). I have two mods for Rome TW (original), one I stick to for Medieval 2. Also I'm using Darth Mod for Empire TW, and as for Shogun 2 even though I've bought it during its release week I still haven't played enough of it to know which mod(s) (if any) would be worth getting, but I'd get one for Shogun 2 as well, I just know myself for that.
The thing about the A.I. in "all TW games" being crap (generally-speaking) is probably because the A.I. coders team has been the exact same over all the years. If they were bad (possibly, not saying it IS the case, but it's possible, it's not because you're being hired by a company that it means you're good at what you're doing). If not, then it looks like they keep hiring people who don't know their job enough or just don't have enough time polishing. I don't want to be harsh toward Creative Assembly's A.I. team by the way, but I'm looking at real-world possibilities. It IS possible that they're just plain bad A.I. coders, period. But I genuinely believe that more than anything else they simply never really had enough time or budget for the A.I. department, because A.I. in video gaming is probably priority zero for most developers and publishers alike.
But despite the A.I. issues I still maintain the thought (and hope) that Rome 2 will be significantly better over the next few months. In a year from now there will be one or two major mod for it and CA will have released at least two, if not more official and big enough patches that most people will forget what vanilla was like at release day. The only exception to that "rule" I believe is Empire TW which by itself is - for me - the least satisfying and entertaining of the TW games simply because I happen to dislike the time period it covers and absolutely get bored of it if I dare playing just two hours even with Darth Mod, but at least with Darth Mod the game is better overall (in my opinion).