... MF will blow up to 16X20 or 20X24 with great clarity, so why go beyond that?
Ignoring the aspects of alternative materials, contact prints and increased tonality and speaking only of silver based film and prints made using an enlarger, you seem to be thinking of the use of different focal lengths only as a means of framing or only as a means of magnifying the image.
You need to think in terms of both, together with the perspective determined by the location of the camera. You find a location that is the one that presents the subject in the way you want it imaged. The level of detail you want determines the focal length of the lens required. The subject, using a lens of a given focal length, determines the area of the negative that is required. Double the magnification of the image to get the level of detail you want and you need four times the film area to have the same subject in its entirety. If you cannot get the entire subject in the frame when you change to a longer lens, then you need a larger negative or you are forced to either crop the subject or accept a lower level of detail by using a shorter lens.
Some subjects have to be printed larger to give the level of detail that you want to show and that means you need a larger negative. Where you think of MF as adequate at 16x20, I think that MF is pretty much done at around 11x14 or an enlargement of 5 times. For me, 16x20 is about the limit for a 4x5 camera. That is an enlargement of 4 times and that is the maximum I will find acceptable when making a detailed print from a 4x5. For a larger print, I think you need an 8x10 negative, also good for about 4 times enlarged. At the other end of the scale, a 35mm negative will, I think, with excellent lenses, go up to an 8x10 without an objectionable loss of sharpness or about 8 times enlargement. So, when an 11x14 print will do and I do not need movements, I use a medium format camera. On the other hand, if I want to print larger or I need movements, I want a large format camera.
Speaking of movements, you may not be familiar with the ability to expand the depth of field that tilt enables, but you probably are familiar with the distortion caused by using wider than normal lenses when you use a wide angle lens to increase the subject area of the image. This is the other significant advantage of having movements where being able to raise the lens without tilting the film plane allows you to get more of taller subjects and less of the foreground without having the buildings or trees look like they are falling in on themselves. Just the addition of these two movements greatly improves the quality of the images you can obtain and neither requires the twisted bellows look. Shift lenses or adapters will help with this to some degree, but, due to the lens lack of sufficient image circle to completely cover the negative and/or problems with vignetting due to the internals of the camera, they are relatively limited in their amount of movement.