Allowing for the consolidation of a single bonus combo, reducing the tank to the same 4 buttons (not skills) of PLD and WAR, does not reduce its complexity in any way. Gnashing Fang, Goring Blade, and Storm's Eye are already differed almost only in how they each interact with their damage CDs, PLD and GNB per minute and WAR per 90 seconds. Gnashing Fang is technically the least complex of the three because it can be woven in at any time where Storm's Eye and Goring Blade cannot. Instead of any manner of compromise, you simply continue to spam 123 and then remember not to hit Burst Strike if Gnashing Fang will soon come up before overcapping. Its sole claim to complexity is via a particular SkS capable of readying Solid Barrel before the nth No Mercy - Bloodfest sync. The rest is the exact same 123 you have on every tank, just shifted over to 456; that's not complexity. It's basic motor function that, in this case, literally cannot be failed. You've harped on about fail checks. This has no fail check. You cannot hit 6 without having first hit 5, nor 5 without having first hit 4.
The reason there is simple: balance is easy when every mechanic (exempting non-mechanics like Darkside, which likewise have effectively no failchecks) is either shared by 75% of the role, has merely excused imbalance due to its infrequency (e.g. Living Dead) or is an inconsequential flavor variant.
When you actually make 4 tanks instead of 4 skins of a single tank, yes, balance gets harder.
That doesn't mean it isn't worth it. We should be able to expect more than just either a modicum of real gameplay difference OR balance.
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tl;dr: If literal hand movement alone is enough complexity for you to pride yourself over, and worth more to you than any of the possible things you could otherwise spend that space on, we're just going to have to agree to disagree.