That's not really true. Power Words, for example, had a casting time of 1. And even Fireball or Lightning Bolt are still a casting time of 3, which is 2 better than a longsword. I've always wondered about these groups that constantly have spells interrupted. I'm not saying you're wrong, just that it's something I never saw.
Considering Large monsters had +6 to their initiative, and anything bigger than that went all the way up to +12, I've always been rather surprised at how often people claim that spells got interrupted.