Well, I can't say it the opinion is popular or not, it does seem like one that's mixed at least.
I can't say I fully agree, because you chose to call it dumb rather than any other descriptor in the title and later on the body, but don't support that label very well in the body of the post. It kinda makes it difficult to accept it as more than a rant, which is not really the same thing as an unpopular opinion, even when the rant is unpopular as well.
My points of digression with the concept you're presenting are that microblogging itself isn't the same as hashtag abuse; and that using the platforms poorly isn't the same as the platform itself being bad.
However, microblogging absolutely does seem to draw a lot of people that use it poorly and abuse hashtags. So, while the underlying platforms aren't "dumb", they sure as hell look it.
I would offer the counter argument that it isn't microblogging that's dumb, it's people; but microblogging shows the dumbness easier than other formats.