I've seen lots of advice to only build inf, cav/vec, and heavy/tank/mech. But why? It makes sense on the offensive, you only build one type of unit-- the one that they have the least counter units for. But for defense? Isn't that like shooting yourself in the foot? If someone scans your colony, and finds out you only use infantry, then they can come in with all anti--inf units. If you have 33% of each unit, then they will have to build 3 types of units to conquer you. Why only build one if the enemy can easily kill all your units fast with the counter type of unit?

well if they have time to build up an army to specifically kill you then it is worse but if they dont they will likely have a good spread of weapons so only a fraction deal 100% damage