From the point of view of a former ET player,
I’d like the revive mechanic to be closer (or the same actually) to W:ET: aka the revived player can’t move for a while and be able to do limited actions, while being invincible.
Something that actually annoyed me in DB is that this immunity can be broken instantly, which make the medic very vulnerable. That “meat shield” as someone mentioned before, was a nice mechanic to play with after reviving someone (even though DB added a “quick revive” option which doesn’t require to switch manually to the defib, you are still vulnerable just because you are aiming the ground, thus losing time to put your crosshair at a normal height again).
In ET, seeing a medic bunnyhop/crouch/revive, then covering behind the revived player while he takes his SMG back (and his crosshair) was usual (even though you could still hit the medic with the weird hitboxes of the game), and it could lead to nice actions in game (chain reviving etc, which is pretty fun to watch). Those actions will never exist with the current system 
In addition, there is no incentive for the medics to take any danger to revive someone on pub servers, you just try to kill everyone at range before trying anything (and in the best scenario, the dead player just respawns because it’s too late…). And that is quite sad knowing that the medics in DB aren’t killing machines (which is ok, I won’t argue about that).