Their rate-limiting isn’t bad at all, their integration into everything is excellent, and for games without much of a community Vortex is often the only mod manager. Their API isn’t closed down, so Mod Organiser can integrate with Nexus just as well, and they probably would also do it with other mod sites if those ever bothered to set up a version check etc. API. They have an excellent search function.
In short: They provide a good service. Like the most annoying part about Nexus as a freeloader is the five or what seconds wait before your mod manager picks up the download.
And, no, their rate limiting really isn’t bad. 1.5MB/s for people with adblock, 3MB/s for people without. How often do you download gigabytes worth of mods it’s not like they’re bullying you into a subscription.