Clearly Sei and Reiji used tactics against Fellini as well and it was called smart but when those brothers do it, it's not as fair since they even incorporated 1/144 Zeon guys to blow up joints.
Tacticians aren't necessarily cheaters, but the spirit of gunpla battles is to fight head-on and the last person standing is the victor. Great strategy in a lot of other battles where you can retrieve weapons after your victory but it's pointless in gunpla battles. Problem was they did not do it properly since they forgot to destroy ALL the weapons (with their bloodhound) and left the 2 weapons that ultimately led to their defeat.
The Renato brothers want to strip Yuuki of all his weapons and it worked to an extent.
