Interesting development though is in CA, insurers are legally required to recommend you a replacement cost coverage amount that is adequate for your place. That probably has a lot to do with the changes you've seen on "guaranteeing" something vs just recommending.
I did run your automated advice system with my recent policy renewal. Reporting was pretty good, although I was surprised that you consider a $3000 deductible "abnormally high". I don't think it's worth trading money with the insurance company as premiums to cover small stuff like that. Not everyone shares my feelings, though.
On guessing rebuild, in CA you shouldn't have to guess, as it's the insurer's legal requirement to recommend something accurate, and the DOI supports the consumer there. Generally those increases will do the job on like-for-like replacement - the big problem is if your Building limit has not been reviewed for years, as they get out of date.
Guaranteed is definitely expensive since it has cost insurers some big claim headaches, so not surprised it's even harder to find now as some insurers are hurting after all the fires.