Very well, i do appreciate discussions, but yeah...i don't want to "convince" you that we got the truth

. Keep in mind that we create our scenarios and games together, we rarely resort to the “make your list I make mine”. Before, we used the game to enhance roleplay sessions. Balance in this game is now an affair of player circles. For us, these work, for you, it might not.
Let's see if i can help you see my point of view (not necessarily agree wiith it, mind you

):
It'll be lenghty, so brace yourself
No more than 3 identical actions The rule is not bad itself but there are some exceptions that make it laughable.
Well lets say I have Golgota, Ragathol, Cardinal Dominic (or any other model with 4 or 5 actions) in close combat with several models and I can attack only 3 of them, and do what with other actions? Swear? Stick tongue at them? Maybe Nepharite of Algeroth should run away from a Wolfbanes?All the models you mention have the ability to do more than just 4-6 of the same. A Nepharite of Algeroth surrounded by troops is not restricted to a mindless butcher. He can sweep attack twice with its azogar (ouch), force his way out of close combat, annoyed, and then shoot his voriche before charging someone else. That's how it can achieve things that mortals could never dream of, but it can fail too (if completely surrounded and unable to kill anything). It’s even easier to do for models with the art or dark symmetry. This makes them act more heroic when you look back at the whole flow by the variety of their action, rather than repetition. Try it

It is extremely rare for 4 action individuals (with the amount of different actions there are) to be stuck, but the rule makes you think on how to get the most of your heroes. I play with Nepharites at times, myself, and have no problem with it at all.
Tell me what will model with 4 or more actions do while: Banzai Charge (Mishima), Frenzy (Templars), Wolfbane Frenzy (Sean Gallagher just died), Sacrificial Run (Lutherans), Invoke Frenzy (Gift of Algeroth)? Can they attack and move for all of the actions or not? We simply decided that 3xM was the fastest something could go per turn. For us, more than that made the game weird. We had no need for individuals to be able to run 20+ inches.
Of all Mishima troops, only Tiger Dragons have 4 acions. The Banzai charge grants them +1Move anyway. It becomes a tactical decision depending on the situation (do they need the CC and ST stats or keep flexibility?) . Granted, Banzai charge’s most powerful asset is that it can be called on Panicking/broken troops, which Tiger Dragons are immune to, so it is rare that they will Banzai, since they are very stealthy troops. There was no complains by our mishima player.
Wheeled Templars only have 3 actions per turn they are not forced to use all their actions to move/charge. As for Karak, he can run a very decent (for us, at least) 15” per turn…and still have 3 actions for the fun of it (2 heavy weapons, dark symmetry…there’s not a chance to loose an action with him

)
Invoke frenzy, like Banzai, already grants a +1M that helps alleviate all movement loss, but in any way, the +3 strenght is extremely good too (most foes will loose their parry!). The most obvious troop with mitigated benefits from the gift are already high elites: Destroyers, Soul Reapers, Praetorian Stalkers pairs (!), Brass Apocalypts). The mitigation stops as soon as they do reach combat though (where the extra AC will come into account)
Wolfbane Frenzy (Sean Galagher) affects all wolfbanes, but no wolfbane troops have 4 actions. Only Wolfbane heroes/heroines do, and they still get +1 Move anyway. As above, the extra action will get used once the enemy is reached.
I do not own Dark Eden, nor anyone I play with expressed any interest to play with its troops, so I cannot say anything about Lutherans’s sacrificial runs.
What About Vehicles with 4 actions they must stop every turn (laughable), Flying vehicles with 4 actions cannot stop, they must move every action. There are only 3 vehicles that have 4 actions, and the only flying vehicle that has 4 actions is the unarmed Pegasus. We’ve not played with it yet, due to the Great Grey requirement. I’ve no doubt we’d come up with something very fair for the little bike : ). Vehicles have extremely high movement already. The slowest vehicle, the GT Offroad, can move 18 inches in 3 actions (the Ilian Cart can nitro ^ ^), which is double that of the standard infantry, and shoots while doing so. As for the Necromower and Fenris Bike, they can can shoot too, so it will very rarely loose the action. It’s up to you to ensure that you can use your 4 actions (it’ll reward the sound tactics, including ramming, hit and runs, shooting etc)
No house rule is perfect, but what troops have a real consequence? Cairaths, Suicide Warheads .
The only troop (that we use) that has a flat out loss with it are Suicide Warheads, but we decided that it needs an action to detonate itself. The test we had still presented them as very dangerous canon fodder (large explosive templates moving 12” per turn for 20 points).
The Cairath comes to mind as well. The reason it is impaired by this rule is that it cannot hide or take extra cover (like Battlehounds of dog soldiers, for example). That said, it is very cheap, has no weapon to pay and its strikes are...a nightmare to deal with. Keep in mind that it will make use of its 4th action as soon as it can do both move and attack in an activation (i.e. when it reaches the enemy), and also when an enemy model hides (it has 15Ld, which is excellent to spot with).
All other troops with 4 actions can do more than just run and fight, they can hide, take extra cover and sometimes, this might entice the player to use often neglected options (Machinator gunner, for example)