I don't dispute that Drilbur is the best weather sweeper that is usable, since I can personally vouch for it. However, I'm still not sold on the claim that it's the best Rapid Spinner. I've never used it though, so it might surprise me, but the reason that I've never used that is because Staryu has always been a better fit.
Defensively, Staryu takes both physical and special hits about 1-2 HP better than Drilbur does, with reliable recovery, a very useful set of resistances to Fire, Water, and Ice, alongside the rare Steel, and pseudo-immunity to status. This is of course factoring in that they are both using Eviolite, as the LO Drilbur set is obviously a lot less bulky but a lot faster and more powerful. Drilbur still has more HP, and that gives it a slight advantage percentage-wise when taking special damage. It also boasts a pretty useful immunity to Electric, but when the premiere Electric-type in the tier is also part Water, that is diminished slightly, but still very useful. Rock and Poison are much less useful resistances than Staryu's. The Life Orb set also has laughable defenses obviously, and the HP it wastes by using Rapid Spin with it, plus the damage incurred from your opponent's attack, means that set gets one chance to spin. If I'm looking for a defensive spinner, I will choose Staryu over Drilbur every time unless I really really need the Electric immunity.
Offensively, I can't fault your argument. Sand Rush, plus an excellent STAB move, and Life Orb simply makes it superior to Staryu in that regard. Water STAB isn't bad either and Staryu outspeeds or ties all common unboosted Pokemon, but the ability to outspeed all +1 Pokemon is a huge boon to any Pokemon. Drilbur is simply superior to Staryu in this aspect. To reflect this, I have no problem calling Drilbur the best offensive spinner, but on the overall it does indeed have some competition.
This thread isn't the Staryu vs. Drilbur debate thread, so I'll just move on to discuss its rank. You've convinced me to take a closer look and I'm definitely on the fence about Drilbur's tier position. Snover, to me, prevents Drilbur from reaching S-rank, since although Drilbur can function in hail, it "defines the meta" with its sand sweeper set. Snover destroys that effortlessly with a powerful Blizzard, so I can't say it belongs in S-rank when its best set is stopped just from another Pokemon existing.
Edit: After using my old team on accident again, I've realized that there are two types of teams out there in the metagame today: teams with Snover, Bronzor, or Scarf Porygon, and teams without. The teams without those three are getting wrecked by Drilbur, and now I remember why I wanted this thing banned. I say it should be S-rank since, although Snover kinda stops it cold (haha), teams without it need really specialized checks to beat it, and if you lack one, you lose!