I’d guess Construction of Light is at least one of them since that’s just about the last KC album every bothers to hear.
Starless and Bible Black is good, but it’s mostly improv and instrumentals without as many composed pieces as the albums on either side of it, so it makes sense why it gets overlooked. KC’s best improvs basically sound like composed songs anyway though so that’s hardly an issue. It just has a bit less to grab onto for most normal rock music listeners.

Mars Volta have never clicked for me. they sound cool enough at times, but i don’t really enjoy their sound much. they just throw an onslaught of sound at you and I admire the talent it takes to perform that stuff but it’s not really a sound that’s shaped in an appealing way. Kinda reminds me of something like Cardiacs a bit maybe (except Cardiacs tunes were chock-full of catchy bits). Its possible that they’ll click with me one day though.