I have listened to many instruments play concertos both with orchestral accompaniment and piano accompaniment.
The piano accompanied soloists sound boring and academic by comparison with the richness of an orchestral accompanied work.
There really is no comparison. Picture a Beatles song with no strings, no percussion, no guitars, just piano. Doesn't work at all. I feel the same thing about solo piano some of the time. It can work, but usually orchestra is better.
The biggest defect, of course, is that to play with an orchestra you must learn to count. Many otherwise talented soloists never succeed in this and are forced to play only solo works.