Ok, I don't know why but I got hooked up on this game fighting mechanics. Here's what I've found so far.
This is not an "MMA" game. This is a boxing game
Forget about the kicks, they are useless. Since fighter number 2 (Rick Wild) they dodge your kicks so often that it becomes more effective to just punch. And punch. And keep punching. The damage boost from the kicks is DEFINITELY not worth the risk of missing. The accurracy % does not consider opponent's dodge, so you will miss A LOT.
Abilities/upgrades tier
S Speed and strength
These make it happen. More attacks and more powerful attacks. They explain themselves
A Dexterity
Makes you miss less. But forget about the % shown ingame, the dodge rate of the opponent is way more important.
B Dodge
This actually seems to work. However you should only invest in this when you don't have enough money for speed or strength
C HP
If you boost the other stats correctly, this stat should only be your safety net, so don't spend much money on this.
Next suggestion
Don't star fighting the second fighter from the moment you can beat him. Start fighting (and grinding him) from the moment you can't lose to him.
TL;DR:
JUST USE PUNCH
Boost strength and speed, dexterity with leftovers
Boost the fuck up before moving on to the next fighter