It’s possible that FiM could’ve gotten somewhat popular but I don’t think it would’ve been the phenomenon it is without /b/. Memes and captions would be born on 4chan, and then spread out as they were copied onto other websites. /b/ was spammed with ponies, and therefore, EVERYWHERE was spammed with ponies.
I was already in the fandom, and seeing memes on multiple forums and games, well before the spamming started on /b/ or the global ban. 4chan isn’t the only place that has people with the creative genius necessary to add text to a screencap.
From what I recall, though there was a purest faction of channers who were anti-porn, porn was more associated with the “4chan side” of the fandom with the “squeaky clean” Equestria Daily tier people trying to avert there eyes and pretend it didn’t exist (sort of) and the earlier lefties types trying to actively fight it sometimes though this would look very weird and you’d find conservative Christains, early social justice types, and apolitical/others sometimes collaborating loosely on it.
From the start, most channers were anti-porn as it was “furry”, and the few artists that posted porn on the board were either trolling, or were already into doing any sort of r34 and knew nothing of boundaries.
It wasn’t until /mlp/ was spawned and ponibooru changed its rules to allow NSFW that that sentiment changed, given at that point the majority of the “channer” fandom were new and not around 4chan when the fandom was spawned, and just gravitated there because it was the most active chan (efchan, 413chan, and stevechan were dead or ghost towns, and ponychan had too many boards and rules and quickly became a shitting-on target for /mlp/).
Even so, /mlp/s obsession with being anti-furry has lead to the harassment and dropping out of the fandom of many furry artists that did pony, or pony artists that started doing furry or too much anthro.
Equestria Daily ran borderline NSFW art roundups for its first two years, and it really wasn’t until the tumblr harpies started crying about icky bronies invading their safe space that those went away.
I don’t think that bad behavior should be excused or them deserving special treatment. I come at this with more of a cultural and heritage angle with this sort of thing though and think that we all share a lot of DNA.
My point is there is no heritage. The people on /mlp/ now have nothing to do with the people on 4chan that could be credited with spawning the fandom. People saying that /mlp/ should be given more respect or slack because “the fandom came from 4chan” are wrong, both because it didn’t, and because nothing excuses the sort of bad behavior people from that board have become known for (at the expense of the majority of the board, possibly, but still what its known for).