but either the devs used some method to give the AI and edge the player didn't have, or the combat was laughably easy.
The combat was so laughably easy, that people were stuck on certain fights for a long time (on normal difficulty) - which almost never happens in today games.
Of course there were hidden advantages that you can use - but the trick was, that those games didn't just put 10 regular guys against your party.
Every major encounter (and there was a lot of them) was designed in such a way, to give the enemy the edge. They had potions, sometimes were prebuffed, battlefield was filled with traps, enemy had good weapons or other items (that you could loot later and use yourself).
Enemies had the same chances that you did - so if an enemy mage casted haste on his party (which then proceeded to murder you horribly), you could counter that by for example sneaking in with a rogue first and backstab - kill the mage. Or prepare a dispel magic spell instead of your fireball. Or just interupt enemy's spellcasting at just the right moment.
The thing is, that those fights had many more options than just launch 20 guys at opponents party and have mage spam AOE, which enemy party is immune to.
They followed the particular path and strategy, which you could of course exploit and distrupt by various means - killing the spellcaster, dominating their main warrior, using summons for cannon fodder, so their mages run out of AOE spells, hurting enemy warriors in the process... Lots of stuff, and it was all done fairly.
Thinking gave you a significant advantage - but you had to think and control your party. Controlling just your main character and rushing in would result in certain death, unless you really knew the system. But for the first-time playthrough? You'd die. A lot.
And none of that felt unfair, like all those damage-sponge bossess in DA series. Or enemies immune to friendly fire.
In general, those games just used less obnoxious ways of giving AI the edge: better equipment, slightly higher level, traps, prebuffs, potions, scrolls, more enemies... You could always of course count for the boss to have more HP and better damage than your guys, but disproportion was much lower than in DA series - so you didn't feel that the game is cheating.
Enemies immune to friendly fire (and having several times more HP) does feel like cheating.