Well, I spoke too soon. Booted up today and it's been 1 1/2 hour and I'm still waiting for it to open a single email. I'm here today on my phone (android).
What makes the system go bezirk is that it registers each keystroke and click: it just takes about 20 minutes to execute. So if I click too often on something because of no response, each click is cued up to bite me later. For example, a "force quit" that didn't seem to register ends up happening half-hour later. Then Safari suddenly opens (clicked that an hour earlier) . Apps are opening and closing, seemingly at will but it's just because it's SO FFING SLOW.
This is a 2016 system. My old 2007 Tiger iMac is still running beautifully. Instant response. The only reason I bought a new one is because of internet access. Old Safari won't work there anymore. Garageband is better on the 10.4 Tiger. New one is a joke.
Tiger was the best system Apple ever made. From that it's been downhill.