Picture lacks sharpness, critique requested

[Designer]

How much better is the 85mm prime than the 70-200mm f/2.8 VRII at 85mm? Is the glass that much better? Is it inherently designed differently?

It depends on which prime and which zoom. Yes, lenses are different. Sometimes it's the glass, sometimes the design, and sometimes both. Learning which lenses are superior is going to take some time and research on your part. Sweat it not, however, because there are sources on the interwebs that will help you. Beware of incorrect information, and learn only from people who know what they're talking about.

 

[Dragster3]

Would someone help me to summarize the improvements I should make to my portrait photography to avoid this issue in the future?

Shoot more pics with different setups. Lots of pics with different settings so you can get a feel of what to do for each situation.
Being able to adjust to your surroundings quickly is what makes you better.
And remember that 200mm is 300mm, So an 85mm is more like a 125mm. Learn to use the crop to your advantage.
Move the subject, try different background depths. Shoot more pics! Digital is free! Upload them to your iPad on the spot
and instantly see if you like the outcome. Don't wait till you get home in front of the PC, its too late.
Good Luck.