In my experience, the crazy broken x-1/x-1 gestalt you speak of was never more powerful than the single classed character in AD&D. Maybe the spells scaled better. But I remember playing many such "gestalts" and finding it more difficult than single classed players.QUOTE]
We found that multiclassing in 2e was always more powerful. Nearly everyone did it if told we got to start at higher level. The only time we chose not to was when we had to start at 1st level. It sucked to be the guy who was still 1/1 while everyone else was 3rd and had more hitpoints and THAC0 than you. You died too easily.
However, if we were told that we were going to start at 5th level or higher, pretty much everyone multiclassed. If we were told we were starting at 15th level or higher everyone dual classed instead.
However, although we found that multiclassing was more powerful, it wasn't on the same scale as multiclassing in 3e. It was nice to have more hitpoints and a better THAC0 for your Wizard and it defintely made them more powerful. However, the difference between a 20 Wizard and a 19 Wizard/19 Fighter was +13 to hit and around 25-87 hitpoints, and a couple better saves in exchange for losing a couple spell slots. The difference between a Wizard 20 and the right combination of multiclassing in 3e might be +8 to hit, 96 hitpoints, 2 more attacks per round, 8-15 points of AC, about 5 more feats, and better saves in every category in exchange for a couple of spell slots.
If you had the ability to plan in advance, it was always to your advantage to multiclass.