In RBY, using X Accuracy on a Pokemon causes all moves used by a Pokemon to ignore accuracy checks (i.e. they always land successfully). When I say all moves, I mean ALL moves, including OHKO moves. This means that as long as the Pokemon is faster than the opposing Pokemon (a requirement for OHKO moves succeeding in gen 1), they will OHKO it without fail. With X Accuracy being obtainable in infinite amounts, this is obviously a powerful strategy that is exacerbated by the fact that both Horn Drill and Fissure are available to many Pokemon as TMs, along with Guillotine being available to a handful of others.
I was put in charge of the RBY in-game tier project towards the end of its run. Naturally, I and the other regular contributors of that project were able to recognise that the X Accuracy + OHKO combo was a powerful asset for anything that got it. Despite this, there was a general agreement since before I took the project over that the strategy shouldn't be weighted heavily when tiering Pokemon in RBY (although it was never explicitly banned in the same way that glitches are banned). Why not? Because it placed a damper on any potentially interesting discussion that could come out of the project by making things too cut-and-dry - it's the same reason why we avoid tiering things based on their ability to solo the game. Allowing the combo placed a risk wherein people would start trying to focus discussion on which Pokemon learned a OHKO move and which ones didn't, and that in turn could lead discussion away from other relevant aspects of a Pokemon's performance and result in an unhelpful tier list, with stuff like Fissure Lickitung and Horn Drill Dragonair in higher tiers than they ought to be.
Why am I bringing any of this up in the DPP thread? Because reading these arguments about Bibarel being in S-tier because of utility alone reminded me of the X-Accuracy + OHKO situation in RBY - essentially, people are attempting to take an otherwise mediocre Pokemon and call it one of the absolute best Pokemon in the game because it's an early route mon with access to lots of HM moves. Comparing OHKO moves with HM compatibility is a huge stretch, but I think there is some parallel in the way weighing a Pokemon's utility so heavily is causing things to be overly cut-and-dry.
By placing so much weight on HM utility in the case of Bidoof, a dangerous precedent is placed wherein every Pokemon's potential utility has to be weighed just as heavily. It is a double standard to shove Bidoof in S tier for its utility alone, fighting prowess be damned, and then have it have seemingly little impact on the final tiering of anything else. Accordingly, by using this approach for Bidoof, you guys are going to have to assess EVERY Pokemon's HM compatibility/utility just as heavily for consistency. I have previously used the example of Piplup in this thread, whose evolutionary family has access to SEVEN HMs, and yet this doesn't seem to have received as much attention as Bidoof's six HMs. Psyduck's family has access to five HMs, and the only one it misses out on compared to Bidoof, Cut, is barely useful after leaving Eterna City if you only care about reaching the end of the game (which is all we should care about for an efficient run), so perhaps Psyduck ought to be raised from its current B-tier. Kricketot's line is early-route and has access to Rock Smash, Cut and Strength, so maybe its "utility" makes it too good for E-tier. I could go on, especially if we start to bring things like Dig and possibly even moves used solely to help catch Pokemon (i.e. status moves).
Alternatively, and more sensibly in my opinion, we could treat Bibarel like every other Pokemon and stop giving it the special treatment I've seen throughout this thread. I would not go so far as to say HM compatibility should not be considered period, but it has to be weighed up in comparison with the usual criteria that Pokemon are assessed by: availability, stats, moves, match-ups and so on. In Bibarel's case, it happens to rank highly in the availability criteria and is an excellent HM slave, and I would argue that its move pool is not half bad outside of its HM access, but it ranks poorly in stats and its match-ups overall are mediocre, which I think is enough to bring it down. Bibarel's battling prowess is mostly limited to being an ok route sweeper, and that only starts being true when it first gets Headbutt (which is mercifully pretty early overall, but as a Bidoof its performance is garbage).
I think that Bibarel should be A tier. It is a convenient Pokemon that can pull its weight against randoms, but it should not be ranked alongside the likes of Chimchar and Starly, who should be in a tier on their own above everything else.