Being spikes weak, incredibly frail to physical moves, extremely slow, and easily switched in on by waters (particularly those with refresh) mean camerupt is very likely to make no progress against teams that have one of its many checks and counters, and even teams that don't don't have a particularly good camerupt switchin usually have some way of pivoting around it. Also, increased spdef Zapdos usage is very very bad for camerupt (sure, fire blast hits reasonably hard, but good luck with four of them). It's not useless but it's a very niche pick that is going to be outclassed on 99% of teams, similarly to rhydon and registeel, which accompany it down there. Blaziken is essentially a matchup fish that does incredibly well against a common teamstyle (classic beerlover has no way to switch into it), so it gets a bit of credit for that.
Perhaps Camerupt should be ranked higher than it is (and a new vr will come out sometime soon so maybe its placement will change) but there's really not much point complaining about where a mediocre-to-bad pokemon is ranked in comparison to other mediocre-to-bad pokemon. Camerupt is ranked higher than Flareon, and only one of those fire-types has seen SPL usage. Also, the ranking of these lower mons essentially has no bearing on anything, as the vr is two things: a reflection of the current state of the metagame and an aide to teambuilding for people who aren't very familiar with the tier. People aren't using much Camerupt, and I wouldn't suggest it to new players either if I had their best interests in mind, so the rankings of most of the mons E tier and below is pretty much just there for the people contributing to the rankings to share ideas and off-meta strategies.
Perhaps Camerupt should be ranked higher than it is (and a new vr will come out sometime soon so maybe its placement will change) but there's really not much point complaining about where a mediocre-to-bad pokemon is ranked in comparison to other mediocre-to-bad pokemon. Camerupt is ranked higher than Flareon, and only one of those fire-types has seen SPL usage. Also, the ranking of these lower mons essentially has no bearing on anything, as the vr is two things: a reflection of the current state of the metagame and an aide to teambuilding for people who aren't very familiar with the tier. People aren't using much Camerupt, and I wouldn't suggest it to new players either if I had their best interests in mind, so the rankings of most of the mons E tier and below is pretty much just there for the people contributing to the rankings to share ideas and off-meta strategies.