This is the most common misconception that I see regurgitated about TC drivers. The key word is relative. Proper understanding of this driver's behavior and proper application considering that behavior is key to successful implementation if you want all around performance. There will be limitations with certain drivers, though, and that is not unique to TC Sounds.
They are indeed bottom heavy. But many of them stretch right out to 2k-3k without any issue other than edge resonance (cone and surround relationship) and cavity resonance (coil former height and pole relationship). Take the SW8000 for example. This driver will straight up play the entire bandwidth between 15Hz and 5kHz which is the epitome of bandwidth (I will gladly make a video to demonstrate this high frequency performance, and yes some of it is resonance due to the aluminum cone). Is it flat? No, but it is far from offensive. No semantics here, I'm just trying to point out the bigger picture. But what you're really touching on is the balance between three areas of performance as it relates to mid bass/bass/sub-bass.
TC has always been bottom heavy and some of that is certainly because of soft spiders. Yes, that also lends itself to lower distortion and limitations on SPL abuse. But that's exatly the balance that Thilo wanted to strike with his designs, I don't imagine cares too much about SPL, lol.
But about the key word - relative. It's up to the end user to put everything together to allow for a balance that has the low end relative to the midbass. Show me someone's setup that is too bottom heavy and I can fix. I guarantee it.
This is meant to inspire someone of the possibility, not me saying that I'm the shit.