Lets just all toss out our cruisers and get mountain bikes to put our motors on because we're obviously doing things wrong.
Dude, think about what you're doing. You are in the CRUISER forum posting in a thread titled "Strengthening my new cruiser" telling the person to get a mountain bike. Why not go over to a roadster forum and tell them that roadsters are weak for how heavy they are, complicated to mount things on, are crowded inside for passengers and have no place to store luggage then tell them to all get muscle cars because they have stronger frames, better brakes, a back seat and a big trunk.
You've made your point, you like MTBs over cruisers, good for you.