The RS212 is not at all boomy... I've used 3 of them together and I have no issue with 'boom'.
I used the RS210 on occasion, alone, and found its sound to be quite lacking in lows and volume (compared to the RS212). It does add a tiny bit of punch in the RS210 RS212 combo, but I tend to just stick with nothing but RS212's and take enough for the requirements of the gig (usually 1-2).
I have yet to try 2 x RS210's, though I can't imagine I'd like 2 of those more than 1 or 2 RS212's...
PS I forgot to mention that everyone who has an opinion on (or owns) an RS210, will disagree with me. But here is my story: when I don't have the amp above half on the master volume and can play a gig with a single RS212, but the same gig 2 months later on the RS210 requires almost 3/4 with about 3 extra clicks of lows to get anything close to the same volume and fullness, its hard to see it their way

And the sound didn't carry nearly as nice on the RS210, sounded thin and incomplete, compared to the RS212.