Yes, 3 hours is the norm and based on my recent MCO experiences, you need the time. First of all ME may stop at one or more resorts on the return trip and then stop at one or more of the other airlines before yours. Also MCO has a "reputation" of long lines at the TSA security check. We used ME in April and August and needed every minute of the 3 hour pick up to make our flight. FWIW we used a towncar for our October trip (Dolphin) and the pick up was 2 1/2 hour prior - direct to MCO from the Dolphin.
I feel that waiting at the gate is much better than stressing on the bus or in the terminal trying to clear security.
TJ
TJ