If you are using a belt properly there is no such thing as "relying on the belt".
A recent study has shown that using a belt DOES NOT reduce abdominal/lower back activation during squatting (like most people believe) AND it actually increases quadriceps and hamstrings activation.
Properly using a belt means using the belt to have something to push on. When you squat you should expend your belly then tense up your abs as if you were about to get punched in the stomach. The belt gives you something to push upon and get tensed more. So if you are using a belt properly it actually help you use your abs MORE.
If you use it improperly, clinching it as tight as possible and not expending your belly and tensing your abs, then yeah, it becomes a crutch.
A powerlifting friend of mine has a cool way of using a belt. He start to use one at about 75% of his max and the heavier it gets, the tighter he puts it. At 75% it barely provides any tightness, but it still give you something to push on.