I'm not sure that any founder should make a decision based on a future prediction of sustainability. Each founder should make decisions based on the environment he encounters when making a decision.
In this case, the imbalance has existed for years and is getting more pronounced. My thoughts here are based on that dynamic. If this changes, then I'd likely change the advice.
Importantly, the imbalance has changed, and the valley has not seemed to hold a grudge. There have been shifts during the recessions, and certainly after the 2000 bust, but it's a fact of life: the power dynamic sometimes changes, and the best deal you're able to get at the time is the deal you are going to get.
It's not entirely unlike mortgage rates, tbh; when you refi matters, due to the rates being variable. When you raise also matters, but sometimes raising is the important part, and the terms are the terms.
In this case, the imbalance has existed for years and is getting more pronounced. My thoughts here are based on that dynamic. If this changes, then I'd likely change the advice.