I would put Solarpunk rather in the accelerate/anti-auth corner of a chart with axes for (anti)authoritarian-iness and pro-/contra-progress as I saw it on Twitter once.
Slow-down/anti-auth is primitivism (think: subsistence farming, no computers, ... ).
Cyberpunk is definitely accelerate/auth (like it or not but we seem to be heading into this direction).
technologically yes (although not as fast), but I think at the same time the assumption often is that the anti-authoritarian move also leads to an intentional "enlightened" slow-down of society (compared to the capitalist rat-race of cyberpunk), reduced nature impact that way, ...
Slow-down/anti-auth is primitivism (think: subsistence farming, no computers, ... ).
Cyberpunk is definitely accelerate/auth (like it or not but we seem to be heading into this direction).