I think the main issue (amongst the tech community) was that they did this with out making it known to users (patch notes don't count - especially with autoupdates, who reads them?) the device just started getting slower.
If there was an option that was presented to users once the device got below 80% battery health to slow down the system to make daily batter life longer, then that would be an actually welcome feature.
The problem was Apple just went a did it, and to a normal non-technical user, that means their phone is dying and they need to upgrade.