So far I do completely agree with you. But the reason Phoenix’s self revive is a hard-to-pull-off ability with such a long cooldown is due to it’s power. When we talk about “power”, we aren’t simply talking damage, it’s about the abilities overall effect on the game and the players. A self-revive in a game which requires team-work and relying on your team-mates for aid, is pretty huge.
With this, it’s completely HOW it works right now. If you can pull off a self-revive and complete the animation, you get the brief period of invulnerability. I’ve lost count the amount of times now I’ve self-revived because people forgot to gib me, then while their backs were turned I gunned them all down - and all the while they shot back, I took no damage. It’s great!
But this is the thing, you have to pull off the entire revive successfully. Phoenix has the same revive animation time as anyone else, so it acts exactly the same as being revived by another medic - so why should being gibbed while in the animation be so unfair? Once you have triggered the self-revive, the 60 second cooldown is in-place, it’s the same principle as using a defib. You use it on the player, you get the “revive” exp, but they can still be gibbed while in the animation. They are dead, you still got the “revive”. Perhaps it’s this mechanic that needs looking at and changing - as opposed to specifically Phoenix? Because that is where I see the problem stemming from. 
And finally, yes, I did understand what you both meant with that. Although I think my explanation on it before-hand is still relevant to the argument. ^.^
Hope this helps sum it up a little more clearly. :3