Nah. You're looking at it backwards.
Rainbow Dash's job handling the weather is directly tied in with her speed. Aside from joining the Wonderbolts, weather control is the ONLY job where she would be free to fly around at top speeds.
Her cutiemark is still about her love to go fast. The weather job is just the only job available that allows her to DO that. To go fast.
I dunno. The fact that he INVENTED a whole library's worth of magic kind of leads me to believe he didn't socialize very much.
And if the key to that spell was friendship, then there's no way he'd have been able to complete it; being the probable secluded loner that he probably was.
Probably.