I'm sorry to say but T-Mobile just cannot keep up with demand if they keep adding more and more subscribers and not enough capacity.
Try using T-Mobile in a crowded mall or stadium or even disneyland. Your signal will not be an issue because it'll be there but you'll have no data or have way to make a call due to overloading.
Once T-Mobile starts increasing capacity then I'll decide to switch back. Right now, I'm willing to pay a bit more and be actually able use my service then to be stuck with signal but no reliable data service.
You've described perfectly the problems I've experienced with my Verizon phone in crowded stadiums. Actually, I think if you researched it you would find that TMO's backhaul is actually better than Verizon's.