A giidoffense always beats defense in every edition of D&D.
This is demonstrably not true for a wide variety of circumstances. Consider a 2 PC example with a melee character and a ranged character against a melee enemy. All have 30ft speed. The melee PC engages the enemy. The enemy has a choice:
1. Disengage and move up to the ranged PC. The ranged PC can disengage in response and the melee PC can move up and attack again the next round. If the enemy insists on disengaging to avoid the OA every turn then this option will lead to sure defeat.
2. Attack the melee PC. Melee PC stands and fights. Ranged PC shoots. Repeat. The question here is whether the melee PC would be better off with more defense or more offense in this scenario. Well, it's going to depend on the exact values of defense and offense and by what percent the parties damage increases from the melee PC doing more damage vs how much less percent damage he would take by going for more defense. Unless you can increase your individual damage alot, it's most likely that a moderate increase in defense helps more in this scenario.
3. Move and attack the ranged PC while taking an OA from the melee PC. Ranged PC will disengage straight back 30 ft. The melee PC will dash and position himself between the enemy and ranged PC (forcing the enemy to have to dash to reach the ranged PC next turn. Unless the enemy starts attacking the melee PC he will get no more attacks off against the ranged PC (at least till terrain forces a movement change) and the melee PC will just OA him to death or if he tries to disengage the ranged PC will just attack him to death as he continues to fall back. Thus, besides the initial attacks against the ranged PC, we are back in a situation where the enemies only real course of action is to attack the melee PC, which makes all the stipulations from option 2 above apply. Essentially a moderate amount of defense will be better unless it's a large increase in party offense that can be gained instead.
*Note, changing movement speeds of enemies or allies and/or giving them resource using movement/defensive/control abilities can drastically change the dynamics. But the point is that a brute enemy with 30ft movement and allies with 30 ft movement are quite common and this is one scenario where we can easily demonstrate that defensive abilities on the melee PC in the right party will outperform offensive ones.
*Also note, adding in more melee allies can also change the value of defense. If the enemy can choose to hit a more damaging less defensive melee ally he will almost always choose to do so (assuming he has that kind of tactical awareness and doesn't have emotions clouding his judgement). So in some sense it doesn't make sense to have significantly more defensive capabilities than your melee counterparts. Even if it makes sense to have more defensive capabilities than your ranged counterparts.