There’s a reason that attribute scores cap at 10 in game, even for Bosses, and it’s not because we didn’t want people to keep playing past level 9. Beyond the score of 11 in your table the statistics of the dice stop following the nice probability curves that they’re supposed to and they stop interacting with Advantage the same way.
Even if it did somehow work, your dice progression is wrong. You need to do some stupid things to keep the average results correct, like progressing from 7d12 to 9d10 then going from 10d10 to 9d12 a couple of levels later. Even then it doesn’t work correctly with advantage anymore. I made a post about it on the old Mightybell forums that someone kindly transferred over when we changed websites.
As for the feats, I’m not sure I like how variable the one that gives you a feat point is. Depending on how nice the GM is feeling then it could either be a free feat point with basically no drawback (like if you go from 2 to 0 in Deception and don’t plan on ever lying) or completely cripple your character (like if you go from 9 to 7 in Agility at level 9, essentially putting you 2 levels behind the rest of the party). With a consistent GM though, it could work.
The “combining attributes” thing is absolutely overpowered, no question about it. Adding dice to your pool is significantly better than advantage, and also stacks well with advantage on top of that.
In the example you gave, adding that extra d8 increases your average Agility roll by 5, approximately equivalent to Advantage 4 on all Agility rolls; which would cost 32 feat points to get a weaker version of in the Core Rules:
4x3=12 from Attack Specialisation (for one particular weapon type) + 4x2=8 from Skill Specialisation + 4x1=4 from Lightning Reflexes + 4x2=8 from Defensive Reflexes = 32 and you don’t get bonuses to bane attacks from those 32 points either
This feat could maybe work if you restrict it to a single kind of action (either Damaging Attacks or non-combat rolls, like Attack/Skill Specialisation) and double the cost to 4 points per tier (non-combat rolls) or triple it to 6 (for damaging attacks).
Sorry to be so negative, I hope my criticism is at least constructive.