I think the fact this algorithm does not take base frequencies of the hashtags into account is a big flaw. There's lots of periodic hashtags. The volume of hashtagged toots is also very low. Although don't get me wrong - there's people who think hashtags have no use whatsoever, but there's #inktober, #mermay, #mastoart, #catsofmastodon which are very much valid and used by real people and not bots and spammers.