I work with quite a few BRRRR investors in Memphis and have managed their remodels with my contracting team as well as connected them to certain lenders. First, switching lenders is definitely an option. Some lenders find this investment strategy risky and are not willing to loan as much as you'd like, and I believe they are either using a particular appraiser or coming up with their own numbers. You can also look into delayed financing which will net you your purchase price plus remodel costs or 70% of the appraised value, whichever is less.
Secondly, I always explain to new BRRRR investors that going for the full turnkey style remodel is not always necessary to hit that magic appraisal number. As you stated, appraisers are looking at square footage, age of roof, HVAC and water heater, electrical, foundation, windows, doors, year built, location. While fancy counter tops, cabinets, floors etc. are nice, they don't exactly pad an appraisal. These items are added to turnkey homes to get a premium rent rate. I'm not saying you don't need to do updates, but going on a spending spree is not going to help your situation.
Your third question is something you'll have to strategize. Put the ones you went all out with on the remodels up for sale on the market, try to get some cash out of it and start over.