You're making a misplaced Goldilocks argument - one that's merely 'less bad', by acknowledging that too short of term limits are bad, but defending medium limits.
I think a lot of what's driving the passion for term limits is the feeling that the real issue isn't being solved - that it's 'corrupt politicians for decades, or term limits', no other option.
And in fact, that's probably the best argument for term limits, but it still falls far short by simply being bad for the democracy.
It's based on a fallacy, that the new politicians will be some 'new, uncorrupted faces', when in fact the system will be more enslaved to the money.
People will get even less happy with democracy at all, as it's a total waste that a lot of 'honest' people run and are lost in the mix while the winners are 'selected' by money.
It's hard for people to understand the problem it seems before it happens. When I've posted this before, though, some have responded 'we got term limits, and it was bad'.
Frustration often drive bad policy. We need to take money out, not patch the problem.