It isn't quite so simple. Yes, a sideways MTM has flaws, but in practice, it isn't so bad. It really depends on how wide your sitting area is and how far it is from the speakers. If the seat furthest from the center is no more than about 30° off to the side, then it isn't such a problem. Many people, including myself, have such a 'flawed' arrangement.
Make sure to read both of these articles:
https://www.audioholics.com/loudspeaker-design/center-channel-speaker
https://www.audioholics.com/loudspeaker-design/center-channel-designs-1
I wouldn't worry about the difference between the size between those the woofers. Remember that the primary job of the center channel speaker in movies is dialog, human voices. Deeper bass doesn't matter. People often talk about how a moving source should sound as it sweeps from one side to other. It should sound as similar as possible among the 3 front speakers. That makes a fine demo, if a bit gimmicky. I think how a sweep sounds is less important than how human voices sound over the center speaker.
Yes, in theory. But in practice, you can vary from that with success.