While Keldeo's power is amazing, it is too easily stopped. Most sets run Surf/Hydro Pump, Secret Sword, Icy wind and a Hidden Power type (Unless it's the scarf). Out of the top 50 pokemon in OU stats for the past month, the following can stop it cold in its tracks (assuming they switch in safely), I'm assuming E-belt/LO because if I say choice, people are going to get into an argument on whether the person can predict or not:
Rotom-W
Celebi
Starmie
Gastrodon
Lati@s
Toxicroak
Vaporeon
Gyrados
Tentacruel
Jellicent
Quick Point, that is a list of pokemon, that can safely switch into SS / Hydro Pump / Icy Wind, ie it does ignore Hidden Power. For example, I would NEVER use Celebi as my sole Keldeo check simply because HP Bug is so common.
Also your list is incorrect.
Rotom-W cannot switch in on either SS or Hydro Pump if rain is up (and it often is). SS does around 50ish so I wouldn't say it "stops it cold" factoring in SR, and the odd but of residual damage. LO obviously does more (although its not seen) so I don't really get it.
Celebi loses to HP Bug which is like the most common Hidden Power I see outside of maybe HP Ice on choiced sets cos people like to run Hydro Pump and Surf sometimes.
Offensive Starmie loses if it comes in on an Icy Wind / HP Bug, and Hydro Pump does a truckload anyway. I really doubt you calced some of this shit, because "LO" (not seen) has like a 68% shot at OHKOing under Rain with Hydro Pump so yea lol, you cannot switch in.
Gastrodon: SS 2KOs if LO, otherwise ur good 2 go
Latios: Loses to SR + Icy Wind on the switch + Follow up HP Bug
Latias: Looks fine
Croak: Looks fine
Vaporeon: Yep
Gyarados: 252 SpA Keldeo Hydro Pump vs. 88 HP / 0 SpD Gyarados in rain: 147-173 (41.64 - 49%) -- guaranteed 2HKO after Stealth Rock - You do not stop it cold.
Tentacruel: Yep
Jellicent: Yep
So really, out of everything on that list, id prolly only consider 6 of them or so safe to the standard Expert Belt Keldeo (im not even assuming the correct Hidden Power every time). That list gets smaller when you factor in LO (maybe 4-5 or so), and smaller still if you factor in Specs (but don't cos thats gives me a fricking headache). Either do your calculations better or someone needs to tell me what "stop it cold in its tracks" means, because for some of the mons on that list, id really disagree with that phrasing!
108 speed also leaves it outsped by gengar, jolteon, alakazam and the lati twins and speed ties with the other muskateers.
Yea ok fine, but Gengar, Jolt, Zam, and Terrakion cannot switch into a Hydro Pump (well Zam can but that brings it straight to sash), and all of the previous + Latios don't like switching into an Icy Wind either. Jolteon is special because it can pretty much only come in on HP Bug, the other attacks either KO or cripple it.
The choice sets will leave it locked into a move. If it had a spammable move, this would be ok but it doesn't.
Since when is a rain boosted Hydro Pump / Surf not fucking spammable :(
Keldeo has a number of checks and counters and weaknesses sure, I don't think anyone is disputing that, but be careful with what you claim Keldeo is countered by, because incorrect infomation really ticks me off.