Against the AI this is doable and indeed largely uncounterable, though for the record if you survive long enough to get it the AI's chances of winning are close to zero anyways.
Against a human opponent... I almost never see three level 6 capital ships, and having three Akkans at once is pretty much unheard of and quite useless until they're level 6. This is effectively infeasible, and you will never see it happen.
well thanks but it actually happens fairly quickly on the Distant Stars mod what with the cap for buying levels upgraded to six
DS has some serious capital ship related balance issues. It works alright if people don't cheese it up, but there are some pretty nasty combos in DS if your opponent is ruthless enough to use 'em. It's a content mod; don't look to it for balance.
If they wanted to balance it out, they could just put an activation delay on the ability. Armistice prevents the activation of other abilities (including armistice), so an activation delay would necessitate a certain "window" between these uses.
In the real game, Armistice is TEC's sole ace in the hole, and nerfing it would essentially gimp the faction in the late-game. The existance of a fringe case like this is mostly an academic dilemma; in practice TEC is struggling for survival in the late-game and needs every scrap of advantage it can get.
