To be fair the OP is looking at used Cornwalls IV which is what $4k ish? In that price range I would personally buy the Cornwall and be happy. I think it is far less of a risk than Tekton which would be much harder to resell. My general thought is that used Cornwalls are a cheap way to get big speaker dynamics without spending big speaker money.
say the other side of the coin, something like the Revel 228be (used pairs for $5500-$6500 right now). I have owned this speaker and it is super refined, commit no sin type of refinement. Without subs they are pretty light in their bass tuning and are a touch boring (great with subs) but “perfect” sounding. Oddly I sold my 228be to someone local that owned a pair of Tektons (pendragon I think) and after a few weeks he more or less said the Revel eclipsed the Tekton in every way including bass impact and detail. I think he was a bit taken back with how good the Revel really was. Having it in your home is a lot different then a demo.
I bring up the 228be because I owned them while shopping for horn speakers. I think living with a very refined speaker makes warts of other systems stick out pretty quickly. my local shop also has the Revel line (328be, Salon) and Klispch line (Cornwall, La Scala) on the floor for easy comparisons.
So it just comes down to what you value most. With money you can have it all but most of us need to chose our priorities. I think the Cornwall is an ok compromise if you put dynamics at the top in that $5000 price range.