Well, crewed vehicles can crew vehicles right (cornercase where you have one creature with power 2, one vehicle with crew 2 and power 4, one vehicle with crew 4)? Still, I agree that vehicles suffer from the problem of being bad in multiples.
Correct. You need a legal target when activating. If all targets are not legal while resolving it does not resolve. So removing the frog while the activation is on the stack, makes the ability go poof.
I always liked
Defense of the Heart
It's a very fair cheatercard which is much less fragile. The opponent can choose to not play a creature or the opponent can choose to attack badly.
Not being blockable is a cheap shot. The question was which worst creature can beat the current one.
In my book this means kills it in combat (over multiple turns) or having an ability which kills it.
ramosian commander