When batch sparging, 190+ water may not even get your grain bed up to 170. I normally aim for 180° sparge water, but sometimes I space out and over do it. I once had it boiling but had a bit of left over RO water that I was able to dump in.
I tried Schaefer 2 or 3 times over the years (more accurately, politely drank one handed to me). The single worst beer I’ve ever had - f!@#$^g dreadful. As in, not fit to boil brats in. This from a guy who pays occasional $ for Schlitz and PBR.
In a true mashout, holding the grain bed at 170F for a period of time denatures/stops all enzyme activity, ‘locking in’ your mash profile (fermentable sugar profile). Raising the grain bed to 170F obviously requires sparge temps considerably hotter. Most homebrewers (myself included) don’t do a true mashout - I got in the habit of doing it also thinking it might increase my efficiency a bit due to reduced viscosity at higher temps. I don’t believe it does to any real extent, but I make good beer thanks to having a handle on pH. The astringency I got came at cooler sparge temps with lax pH control, ironically.
yes and no. It control of pH will lessen the risk of tannin extraction a lot but as Martin and Jeff have both found if you go to far trying to squeeze those last efficiency points out you still risk some astringency.
but generally speaking, yes, pH is more important than temp.