Rock, paper, scissors is always a good idea in combat systems. It allows to win, even if you are weaker, however being much stronger will let you win even if you are fighting using "scissors" vs "rock". 4 openings are oke. It makes fighting interesting, and sometimes unpredictable buuut you still can counter everything with proper skill.
In actual system I see these problems:
-everybody do this: pick STRONK SORD! or BIG AX! grab AS MUCH ARMA AS YOU CAN! pump up STR, AGI, melee, UA, go kill somebody. Has somebody ever seen bows in battles? or low armored warrior with spear? I mean, there is only one way to fight now. Rock, paper, scissors would fit here perfectly to let us see better variety of fighters. For example: swords could do much better damage than axes (or blunt weapons) buuuuut they would also have very little armor piercing (its logical right?), while axe (or blunt weapons) would do smaller damage but could much more easy pass through armor. Pointed weapons (spears, or other long weapons) could do low/med damage, and have low/med armor piercing but could be able to attack for distance of 2 tiles maybe? (not sure if it will not inteferre with fighting through walls that could make killing animals too easy but its just loose idea). About archers later (but they will become useful now). So we have RPS system for weapons- swords beat low armored, axe/blunt beat armored.
Now, why wouldn't we even think about not using heavy armors? It's simple heavy armor makes you move slower (like in real right?). I can now see how you all cry "OMG NO! WHAT A STUPID IDEA, YOU CAN BE KITED THIS WAY EASILY!". Ofc you can be kited, buuuuut! Hey! It's heavy armored knight. This works in many other games. Think about purpose of wearing such heavy armor. They could be worn in specific situations- for example when you know, that noone is going to run away (Yes! Sieges! Yes! Fighting trolls, bears maybe) That's the purpose of heavy armor. Now even a common bandit is wearing full plate O_o wtf! Ofc there sould be lighter armors that could give you reasonable protection buuuuuut weak enought to get pierced by sword and arrows and spears ofc.
Heavy armored knights are oke, but look at them like a tanks. Tanks are strong, they are terryfing, they can hit buuut single agile soldier with grenade can destroy it, right? That's why they are always with infantry support. Sooo heavy knights- tanks, light armored- infantry. This gives us better variety of fighters. Don't forget about archers. We will now have situation like this- slow moving heavy armors accompanied with light ones want to fight other group like this. What do you do? Just go and kill each other, bring some archers, and try to take down light ones first, to let your blunt weapon fighters finish those knights. But then they can hide behind knights and continue charging. As you can see this would make combat more complex and add greater variety of weapons/armor compositions. And will place a seed to begin more advanced tactics than just "CHAAARGE!!! KILL THEM ALL!".
-Oke. Next thing. It is common that you can't even do 1 damage do the player, even if you have 200+ stats (I know in late game it's not very much, but it doesnt matter). In my opinion the damage values becomes too huge, without any ability to defend very often. What can we do with this? Well, we have openings, but they do nothing except being colorfull. What do you think, about making them affect the battle actually in other way than just let you do damage?
Red openings could lower your damage output upt to -50% at 100% opening.
Blue would lower your atack speed up to -50% at 100% opening.
Yellow may lower your atack weight up to -50% at 100% opening.
Blue could lower humm... there are 2 posibilities- movement speed, or effectiveness of the defence (armor, parrying or both). I would completely remove IP value. We have local cooldowns, that can do the job of disallowing too many cleaves etc.
We should lower the top damage values and raise lower ones. Not sure how exactly (maybe with those openings). This will surely add more ballanced gameplay.
We could think about even removing the whole window with openings, and use targeted atacks like its made with bow. Openings could be visible as small icons, colorful lines, above each character. Atacks should have a bit greater range to do this, and there should be a way to easily follow a heartling to let you aim easily. Dunno if its technically possible, but could make fighting more interesting, make positioning important. Players in part would ofc not be able to hit each other. This way spears with little longer range can be useful in teamfights.
-I would add a wae to shoot from inside of walls. For example- watch towers. Standing on them, would give you a boost to arrows range, and ability to shoot through walls. This will allow you to defend againsts sieges a little bit easier. It should be able to be built only by permissioned villagers (like banners, so enemies can't build their own towers in front of your gates.
No idea what from this ideas you will like, but maybe will give you some inspiration for your ideas or something. That's what I'm thinking

Regards!