Unlikely because (I'm like 99% sure) you have to do story missions to unlock strangers+freaks missions, and more story missions to unlock those if you know what I mean. It'd essentially be 100%, but without the hobbies and activities.

You probably forgot that "The Last One" is also a S&F mission and unlocks only after a player achieves a 100% game completion, so yeah. No way.

does the last one count towards 100% speedruns?

@MiloDaKat no

It would be a 100% speedrun with an extra mission on the end

I do think a modified 100% run where at least a good chunk of the non-100% side missions, especially Michael's and Trevor's, are done. Also this would be probably the closest anyone would be willing to go for a true "social club%" run, as only the submarine parts technically are part of a s&f mission, and they can easily be obtained without necessarily needing to travel around the entire map in the designated vehicle. Also Trevor is driving towards his house if option C is chosen after the credits; the Mrs Phillips mission can be immediately triggered, and the city hospitals have the needed vans upon respawning at them.