I wouldn't say it's heresy at all, and you'd likely be correct for some (maybe most...I don't know) of the people, some of the time. But a cold comparison of the specs and FR response graphs between the similarly priced SVS 2000 Pro Series and the REL T9i show that the SVS is clearly the better performer at that price point. The relevance of that information to anybody in their real life situation/room is a matter of personal preference and, to some extent, how much time one wants to put in on integration, etc. But, it appears to me that, everything else being equal, with some good effort and knowledge, one would likely get an audibly better result with the SVS 2000 Pro vs. the T9i.
For me, at this time, it's not a matter of upgraditis, but a need to replace what appears to be a failing sub. My own preference is to buy the best performance for the money I'm willing to spend. I have both the time, inclination, and enough knowledge and experience integrating the two R-305's to be willing to take the time to fiddle with (whichever) the new subs, measure, remeasure, reposition, etc., etc., and "get it right". Aside from the specs, there are some aspects about the SVS (the DSP and phone app) that make it especially appealing for that integration process....having spent many hours with the REL's on my knees, within inches of a working sub, counting gain and crossover knob clicks (REL owners will understand, heheh) .