I've literally never seen "OTOH" in my life. Anyhow, if you really feel your sentence can't do without it you can say "conversely" which is pretty short and clear.
It also isn't an exact synonym of "conversely".
I've been an extensive internet user for decades and I don't have it in memory, so I'm not sure how to feel about your assertion. I'm not the only person saying this.
I'm sure that depends on the tolerance. "assist" and "help"? "dog" and "canine"? "purchase" and "buy"?