Thanks for your thoughtful comparisons.
IMHO
It seems with the expansion of luxury expedition ships the availability of good expedition staff has spread out. Whilst most ships will usually have a few top members with local knowledge, the balance are now just zodiac drivers. If you're lucky you will get a good driver who is at least entertaining and made an effort to learn something of the local flora and fauna.
Exceptions apply to this generality. On a recent Fiji to Broome, the first leg was one the best expedition teams we have ever encountered, the second leg after a change in Cairns paled by comparison. Perhaps the luck of the draw and not specific to any one cruise line.
Over the years we have often seen some our favorite expedition staff bounce between Seabourn and Silversea. We now see some on other cruise lines. Perhaps the lure of better accommodations, different itineraries, and of course money.