Ask yourself why Keldeo's use has been quite low this gen. One major factor is the existence of Talonflame (whose existence also spikes Rotom usage too) and that can tank Specs Sword and Hydro Pump too.
Just for clarification, you're talking about Rotom-W tanking those Specs moves, right? The way the parentheses are set up it looks like you're saying Talonflame tanks Keldeo's STAB's, which obviously isn't true.
(The following calculations use Timid Keldeo, and are purely to show how hard Keldeo hits.)
Talonflame doesn't want to switch into Specs (or non-Specs,) Keldeo, but it easily revenge-kills him (even without a boost or boosting item.)
252 SpA Choice Specs Keldeo Secret Sword vs. 4 HP / 0 Def Talonflame: 137-162 (45.9 - 54.3%) -- 52.3% chance to 2HKO
252 SpA Choice Specs Keldeo Secret Sword vs. 4 HP / 0 Def Talonflame: 137-162 (45.9 - 54.3%) -- 50% chance to OHKO after Stealth Rock
252 SpA Choice Specs Keldeo Surf vs. 4 HP / 0 SpD Talonflame: 594-702 (199.3 - 235.5%) -- guaranteed OHKO
252 Atk Talonflame Brave Bird vs. 0 HP / 0 Def Keldeo: 312-368 (96.5 - 113.9%) -- 81.3% chance to OHKO
252 Atk Talonflame Brave Bird vs. 0 HP / 0 Def Keldeo: 312-368 (96.5 - 113.9%) -- guaranteed OHKO after Stealth Rock
As for Rotom-W, it still needs to fear Sacred Sword. It can switch in on any other move if Keldeo runs Specs, though it can still expect to take a chunk of damage in the process. This changes if it's physically defensive, so I'll show calcs for both.
252 SpA Choice Specs Keldeo Hydro Pump vs. 252 HP / 252+ SpD Rotom-W: 92-108 (30.2 - 35.5%) -- guaranteed 4HKO after Leftovers recovery
252 SpA Choice Specs Keldeo Secret Sword vs. 252 HP / 0 Def Rotom-W: 195-231 (64.1 - 75.9%) -- guaranteed 2HKO after Leftovers recovery
252 SpA Choice Specs Keldeo Hydro Pump vs. 252 HP / 0 SpD Rotom-W: 126-149 (41.4 - 49%) -- guaranteed 3HKO after Leftovers recovery
252 SpA Choice Specs Keldeo Secret Sword vs. 252 HP / 252+ Def Rotom-W: 144-169 (47.3 - 55.5%) -- 17.6% chance to 2HKO after Leftovers recovery
Rotom-W can hit back pretty hard with Volt Switch or Thunderbolt, but doesn't outspeed without a Choice Scarf.
The point of all of this was just to show that neither Talonflame or Rotom-W is a totally safe switch-in for Specs Keldeo. I'm not entirely sure exactly which you were referring to so I covered my bases. Nonetheless, Talonflame definitely inhibits Keldeo's usefulness by serving as an absolute revenge killer to most sets that can tank a single Secret Sword if SR isn't up (albeit pretty poorly.) Rotom-W can take Hydro Pumps pretty well, but if it switches into Secret Sword it may very well fall before it can hit back.
Edit: Tying this all into the topic a bit better, I think Keldeo is underrated, or at the very least underused in comparison to how useful it is. It still hits hard, has pretty good speed, nice STAB's, can be run alongside Politoed if you really want Drizzle (Politoed is still pretty good too,) and though it doesn't like Talonflame, there are plenty of answers to the bird.