The worst were the Wilson’s. Magico’s were overly deadened to my ears. Anyway, just saying I hear a dramatically improved sound with a well done wood speaker. Harbeth uses this approach as well I believe.
The founders of Harbeth and Spendor did a lot of pioneering research into cabinet materials. Both companies now use cabinets made of MDF - and both are widely regarded as producing some of the most lifelike mids in the biz.
The problem with solid woods and ply woods is their inconsistency, their susceptibility to warping and greater difficulty in machining. Even voidless birch ply will have slight variations between batches that can make it difficult to create a consistent sound. Musical instruments suffer this same problem. I've played brand new guitars of the same make, model that sounded very different from each other, even after professional setup.