I've always heard this sentiment when talking about Dunsparce in battling terms, but I really don't get it. Am I missing something? At least in Gen 6, it is an early-game POWERHOUSE. The fucking thing gets Yawn at level 16 and Serene Grace Ancient Power at level 19. It can destroy the first gym with Rollout no problem and even put up a fight in the second by spamming Roost/Ancient Power. It gets a bit screwed by the third, but that's already dabbling in midgame territory.
I have a feeling this "Dunsparce sucks" sentiment is just brought about by shitty placement. The poor thing is so rare and so often shoved into the mid or endgame that there's rarely (if ever) any reason to use it, but if you put it near the beginning of the game it becomes a very useful tool very quickly.
Dudunsparce has done wonders for its battling reputation, at least, which I am quite thankful for. Hyper Drill is a great move that actually makes the poor thing usable and I find its digging behavior in the overworld very memorable. Genuinely glad that Dunsparce got some love, it's one of my favorite things about gen 9.