I think they should just give all of MKs moves really bad priority so they clank with most other moves, that way he's a character with fast, decent ranged moves and gimps well, but can't kill outright and has bad priority, which would be a pretty unique character.
Priority doesn't work like that.
You can't just assign a move priority. Its all governed by a few factors.
The only TRUE priority is on grounded attacks. That's when you can see something actually outprioritze something in the true sense of the meaning. A ground move's priority is determined by how much damage it does; within a certain range of % it will clank with any other ground move (I forget the range). So basically if I have a move that does 10% and you have a move that does 13% they will clank with each other. If I do say, 5% and you do 20% you will beat my move out due to the huge difference in damage.
In the air everything is determined by hitboxes and hurtboxes. Damage doesn't matter; as long as you can reach your opponent's hurtbox before they hit yours you will win. So long range aerials have high "priority" as do really quick aerials. Marth or Ike's Fair have a lot of priority because of how far they extend their hitbox without putting a hurtbox in reach. Luigi's Nair has high priority because it is so quick and hits frame 3.
It also explains why Falcon is considered to have such low priority due to how all of his moves tend to have large extended hurtboxes.
Invincibility, super armor or heavy armor will allow you to win out even if you shouldn't have by the other rules just because it allows you to ignore KB and stun.
Other then that there is also transcendent priority, and that the special effect MK has on almost all of his moves. In almost every situation it is a great thing; he can't clank with anything and will only be beaten out if you can hit his hurtbox first. Though it gives him a distinct weakness to projectiles. Every other character can cancel out at least some projectiles (some like G&W or DDD can cancel out a large majority) by clanking with them and that is something MK can't do at all.
Having TP on his aerials really doesn't do much as far as I know... Aerials are governed by hitboxes and hurtboxes, so the only thing that really matters in direct aerial combat is the range the moves have. Only way to lower his aerial priority is to give all of his aerials no range... bad idea. You could take away the TP on his ground moves where it would actually make a difference but then you just allow him to cancel out projectiles like every other character. So you get rid of a good thing but introduce something potentially more rewarding for him.
i need a volunteer to test a pac which is mostly for amusement purposes who knew how to moonwalk well in melee
(I can't test on my wii currently)
*drools* I'm all over that next time I'm at my Wii! That is too good Shanus, too good! I hope that works out correctly!