Last bear market was there talk along the lines of 'the bottom won't be in till all the altcoins are utterly rekt'?
I understand that you seem to be asking a rhetorical question, but I will answer anyhow, and that answer is: No.
So, it raises a decent point about whether such altcoin reckoning is a necessary condition precedent before BTC prices can rise or not? Seems to me that the answer to my revised question is no, also, even though BTC price dynamics would likely be on stronger grounds for greater upwards movement with such shit coin shakening.... but also seems to wishful to hope for such to occur because the world does not tend to play out with such purism and clarity.

This time around there would not be complete altcoin reckoning as long as there are funds with low cost basis in those as long as those funds have some positive fiat cash flows.
Some of those funds are highly concentrated in a particular alt (or a small group of them), hence they would defend their initial position(s).