The best bike for commuting is whatever you enjoy ridind the most.
I too commute on an mmmBop, in (almost) full off-road spec 🙂 – 14 mile (~20km) mildly hilly route, takes me ~45 minutes.
The only changes I make for commuting are Continental Travel Contact (folding) tyres and a 48T chainring to give me a higher top-end ratio.
Granted, it’s not as fast as a road bike would be (having said that, there are guys on road bikes I pass on my commute 8) ).
I could probably get to work 3 minutes quicker on a more ‘suitable’ bike, but I love riding the mmmBop so I don’t care.
An added bonus is that I can lock my bike in a very secure & covered private bike park whilst at work, so thievery is not a concern.