I don't think performance/load has ever been a real reason to only serve partial content. The actual reason has always been getting users onto the site where you can deliver advertising more flexibly along with analytics.
For my extremely minimal site, the RSS feed is still smaller than normal pageloads because it only has graphics by reference. RSS readers scrape surprisingly often, but the file is small and highly cacheable, and most of them do a HEAD request only initially and never ask for the file if it hasn't changed. Despite accounting for a large percentage of requests, RSS clients account for only a small portion of traffic. The cool thing is that a lot of these RSS readers are shared (commercial feed readers, ttrss instances, etc) and so they are caching the feed on their end and actually saving me bandwidth vs an equivalent number of users accessing the site directly - a lot of these put the subscriber account in their UA string so I can see that e.g. Feedly is making regular requests during the day but has 30-some users behind those requests. It's a better deal from a cost-perspective than those 30-some people checking each day.
For my extremely minimal site, the RSS feed is still smaller than normal pageloads because it only has graphics by reference. RSS readers scrape surprisingly often, but the file is small and highly cacheable, and most of them do a HEAD request only initially and never ask for the file if it hasn't changed. Despite accounting for a large percentage of requests, RSS clients account for only a small portion of traffic. The cool thing is that a lot of these RSS readers are shared (commercial feed readers, ttrss instances, etc) and so they are caching the feed on their end and actually saving me bandwidth vs an equivalent number of users accessing the site directly - a lot of these put the subscriber account in their UA string so I can see that e.g. Feedly is making regular requests during the day but has 30-some users behind those requests. It's a better deal from a cost-perspective than those 30-some people checking each day.