I would not use MDF for ANY project that I cared about. Especially one I would hope would look as good and last as long as wainscoat. If it ever gets a significant bump or gouged it will be the devil to repair. It is not forgiving of damage.
A couple of years ago I made wainscoating for my dining room. I do not remember just what wood I wound up using, clear pine, fir or whatever I found that was the best. The top chair rail was shaped and you could not do that with MDF. I also used quarter round and plywood. In all I used over 120 seperate pieces of wood.
George, I'm sorry you feel that way. The last thing I would want is for you to think I would use shoddy materials. Being a composite you might think that MDF is pure junk. But in reality, IMO, it is the perfect material for painted mouldings and wainscoting, and I'll tell ya why.
*It's consistent in density with no voids.
*There is no knots.
*There is no grain.
*It's harder than pine or poplar which lessens its ability to be damaged.
*It's easy to repair as fill adheres well and can be touched up.
*There is no movement issues.
*It's consistent in thickness.
*It requires no surface prep in sheet form.
*It cuts and shapes easily and can accept most any profile.
*It glues well to other substrates and to itself.
*It's easier to store (versus lumber) when intended to be cut up for moulding.
For now those are a few reasons I use it. Care has to be taken in handling and fastening.