A full reinstall managed to fix that crash-on-startup for the 6.9 update.
Everything seemed alright at first--with the exception of pop-ups and damage numbers seeming like they were moving in slow motion-I was even getting around 20+ more frames than usual.
However after dicking around in lower tiers for a few matches to get my head back into the game, I jumped into a t9 match and... froze so badly that I couldn't even tab out of the game. So, I forced a quit using alt-comm-q, booted the game back up, waited through the map loading screen and crashed again immediately, this time to desktop. No error messages or crash reports. Loaded in a third time and managed to play for around 5 minutes before getting another CTD without any crash report.
Before, I could play maybe one or two games back-to-back without crashing (with an error message), but it seems to be happening a lot more frequently lately, and seems to happen more in higher tier matches.
Could really use a hand with this; I've got no idea what's going on.