Most people don't need to tow 4000 lbs period. If I had a Maverick and needed to tow 4000 lbs I would absolutely do it though. I've towed more than that in an older Tacoma that's not that different from the Maverick. Would I do it at 75mph? Probably not. Would I be towing 4000 lbs going 65 up an 8% grade in the heat at high altitude in Arizona? Again probably not, but the idea that a small truck needs to be able to do everything is just against the concept of a small truck. If you must have the ability to do that, get something bigger.
I agree that the Maverick's bed is small and the back seat is small. IMO they would have been better off making a regular cab or an "access cab" thing with two doors and fold-down seats, and used the extra length to add to the bed. Those are great if you're single or don't have kids, and you just need to carry passengers very occasionally. If you're regularly hauling kids around you definitely want the next step up. A lot of tradesmen essentially never even use the passenger seat though, and the back seat is just lost bed space unless you're using it for locked storage.
I agree that the Maverick's bed is small and the back seat is small. IMO they would have been better off making a regular cab or an "access cab" thing with two doors and fold-down seats, and used the extra length to add to the bed. Those are great if you're single or don't have kids, and you just need to carry passengers very occasionally. If you're regularly hauling kids around you definitely want the next step up. A lot of tradesmen essentially never even use the passenger seat though, and the back seat is just lost bed space unless you're using it for locked storage.