Harbringer
Your A One Flower Garden
That problem can be fixed just by changing what server your on. I agree that restricting classes is generally a bad idea, but on instant spawn, goldrush/dustbowl servers, not even a good uber or two will be able to get through 3 or 4 sentries especially if there is a couple of snipers, demos, soldiers or pyros for support.
The whole balance of the game was that there was always a way through.