There is no "I win" button. Using spells or other unusual abilities creatively is a tactical and imaginative challenge as much, if not more so, than battlefield maneuvering.
While forcecage is powerful, and probably should have some sort of defense available, trapping your foe in an impenetrable, immobile cube for 2 hours/level is a far cry from defeating them, particularly if they have friends.

To answer in order
1.) Our group for a long time wasn't big into "dungeons", so most adventures were short "hideout/minion/boss" style excursions (kinda like the Delves today, but with a purpose).
2.) 2e. 1d10+casting time-dex mod per round. Declare action before init is rolled.
Fighters were just there to stop quick baddies from stabbing mages while mages descimated foes with fire & lightning. Sure, the fighter might get the killing blow, but he probably did less than 20% of the total damage to the foe.
There is no "I win" button. Using spells or other unusual abilities creatively is a tactical and imaginative challenge as much, if not more so, than battlefield maneuvering.
Esp. if the "BBEG" you forcecaged turns out to be the minion of the real BBEG, who is now stomping on you because you've used all your spells.![]()
I wonder whether it would be possible to re-introduce the "I win" button, but in a way that would avoid the two problems mentioned earlier. For example:1. "We Win": The idea here is that a spell might make the wizard good, but it makes another character better. It is not a new idea - even in 3E, there were some suggestions that knock should give a bonus to Open Lock checks, while invisibility should give a bonus to Hide checks. So, even though a wizard could cast these spells to open locks and sneak around if there was no rogue in the party, he would be better off if there was a rogue, and he used them to improve the rogue's ability instead.
2. The Narrative Win: Here, the "I win" button becomes a plot point, not a challenge. The wizard can, with a single spell, kill the BBEG in one round. However, before he can do that, he need to find the BBEG's true name. And he needs to find a rare component to power the spell. And he needs to fight through the BBEG's minions and henchmen before he can get close enough to kill him. And the party doesn't get any XP for killing the BBEG, except maybe XP for completing a quest. The lower the risk, the lower the reward, and in any case, they should have earned enough XP in the process of fulfilling all the conditions for casting the "I win" spell.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.