scottjenson@social.coop true, although I will say from experience that there are levels to how much people are willing to customize their instance.
Speaking from 10+ years of NodeBB (which didn't federate for nearly all of it, so keep that in mind), admins are able to, in order of difficulty:
pick a bootswatch skin (this instance I am on uses the "Brite" bootswatch skin)
drop in any amount of CSS to override anything
drop in any amount of SCSS if that's your jam
drop in any amount of javascript that is run after everything else is done
change/override bootstrap's variables.scss (this instance I am on overrides the primary colour from a bright green to the ActivityPub pink)
create your own customized theme to change absolutely everything about the site including templates, js, css)
Those first two are the biggest ones due to their ease of adoption, and overlaying additional CSS doesn't require too much engineering effort, although I am speaking in hindsight.
Also, you'd be surprised what people can do if given a textbox and told to write their own CSS. ha!