SVS Prime and Ultra centers both seem to be 3-way so they'd probably be fine.
Toole talks about this in his book in section 7.1, but the stereo phantom center is significantly compromised. Comb filtering causes an audible null at ~2khz, among other things. It's too long to quote big sections, but, "A center channel avoids the timbre problem, stabilizes the soundstage for more listeners, and is less sensitive to room effects."(pg 165,
Sound Reproduction)
There is no real question that a properly placed, identical to L/R center is superior to a stereo phantom center. It just is. The issue comes when you are comparing a compromised design, poorly placed center, to none. Then I agree, sometimes none may be better, at least for an individual listener.
Buy good centers and make sure you can get them <10 degrees elevation difference from the L/R and there is a clear, audible benefit.