Regardless of the source of the idea, I think it has merit. Details would certainly need to be refined, but it could work very well in Gladiabots, if done right.
Regarding the issue of flee breaking the attack: easily resolved by making the total attack time take less than 1 tick. If it gets close enough to attack, the attack will (almost always) land because even if the enemy bot flees, the melee bot won't detect it until after the attack ends. Shotgun might be fast enough to "dodge" completely, but other bots wouldn't be, though retreat could reduce the damage.
Regarding making it a "tank", one option might be changing it's health and/or shield stats based on the melee bot's current action. Make it all but invincible when idling, slightly tougher than mg when moving, and slightly weaker than sniper while attacking, just as an example. Something like that would make it a serious threat, without making it op, and make it have very unique AI considerations on both attack and defense.
Personally, I'm on the fence on this, but I think it's an idea that deserves more positive feedback and attention than it has received so far