Hock Master- in general, being sheltered is better. But everyone is different. That is why there are many Yeshivas for many types of kids. You have to go to the Yeshiva that is right for you.
My guess (although I could be wrong) is that the reason why being in a more “sheltered” Yeshiva didn’t work for you may be because you weren’t completely sheltered to begin with.
But whether or not that is the case, just because something didn’t work for you and doesn’t work for everyone doesn’t mean that it’s a bad system. For most of the kids I know who go to (or went to) Lakewood Yeshivas, it worked out great, and it was great for them that they were so “sheltered”.
But no one system will work for every single person. That would be impossible.