It's definitely possible to make slow server-rendered website. Most of the slow client-side apps are slow because they're waiting on slow network requests.

(I still very much support fast, simple HTML websites. The good ones are a fantastic user experience)

but the host (the company) will need to pay the price in the form of server equipment. Not the user as is the case with client side rendering. If server side rendering becomes slow it will affect all users regardless of their hardware or connection, prompting earlier response from management and devteams.