You talk as if jirachi couldnt afford a fail. Steel/Psychic typing and solid 100/100/100 bulk means that jirachi is not as reliant on it as you think and if all else fails wish+protect can recover your health so you can try again.
We get what you're trying to say, but going back to what vyomov said about Jirachi being able to possibly paralyze Keldeo next turn, is true to what Halcyon said on Jirachi's dependence on hax. It's true that Jirachi would still be a very useful Pokemon if it didn't have the ability Serene Grace, since it could just run T-Wave, but one of the biggest reasons that Jirachi is so threatening at times is because of its dependence on hax. I think any seasoned battler has had that time when Jirachi takes out several of their Pokemon from flinch hax alone. The paraflinch strategy is just so deadly. Still, I've had times when the opponent relies on Jirachi's para flinching to overcome certain Pokemon. It's absolutely true that Jirachi has very solid defense and can possibly recover back its health next turn, but vyomov is hurting your argument by arguing that hax alone allows Jirachi to overcome Pokemon that would normally slaughter it. Jirachi is really versatile and amazing in this meta, but versatility doesn't necessarily make it a good Pokemon.