Percentages

You can achieve two goals at once.

How will you achieve balance with percentage-based protection? Even characters with a 75% chance of success, for whom this protection is necessary according to you, can be defeated after the first attack if they are unlucky (unlike regular protection, by the way). I don't see how this achieves the second goal. Unless the GM adjusts the numbers to "balance" the situation, but since we are playing based on mutual trust between the GM and the players, we can assume and hope that such situations do not occur.