Interesting question. The only thing I can think of is proficiency in the use of the pony should be good with a solo diver but not necessarily. Alot of solo divers either sling the pony or have it permanently fixed in place so even this isn't useful for our work.
I really don't consider PSD anything like solo diving. A good tender can be better than a good buddy. He has his full attention on the diver, can often identify snags before the diver is aware, can determine if the diver is excited or not, his air consumption, depth changes or buoyancy problems, his state of mind and more -- even without voice comms.
I could even tell a diver was cold once because I could feel him shivering through the tether - he didn't even realize it himself until we surfaced him.
A standard dive buddy often has difficulty paying as much attention. This is also apparent both pre and post dive as well.
The tender is your buddy.
I don't want to get into a solo diver debate but the most important peice of equipment that a solo diver can't carry as a redundancy is another brain. If a solo diver ever looses it he's dead, nobody can bail him out