Tactics for Rampart.

The Swamp is the weakest castle for the Barbarians.

Well, I wouldn't say that. It's probably not the weakest castle; rather, few people play as them, so it's difficult to judge their strength based on statistics.
And while the Citadel's tactics are indeed quite diverse and depend on many parameters (including luck), I wouldn't dismiss the Swamp so easily. :)
In my opinion, specializing in Defense gives the army tremendous resilience. For example, Tazar, upgraded to level 10, reduces the damage dealt to the Hero's troops by 22-23 percent. And with a favorable combination of circumstances (for example, expert Earth magic - casting such a simple spell as Shield), the damage is reduced by another 30%, which means a total reduction of more than half.

It only makes sense to use them on medium and small maps. But why? Because magic has always been dominant in Heroes 3. As is known, in these castles, magic is only up to level 3. In my opinion, this is a HUGE MINUS.

What's the problem with building a Guild of Mages in one of the captured castles?