Focus looks good. You might get a bit more detail if you had more subs, but fortunately, globular clusters are fairly bright, so getting a good image with 1 sub is possible.
I'd have to be obnoxiously picky to criticize, but if I must, a couple of the stars have a bit of jiggle (or possibly edge issues) and the center of the cluster is ever-so-slightly washed out. A "normal" person would say it is a very good image. I prefer to be normal.
I still think it is the instability of your deck. It will amplify the slightest shaking from wind or someone walking in the house.
Washout means too long exposure. If you want stars, not faint nebulosity, you don't need 800 ISO (how long was the exposure?). Try again with 100 or 200 ISO.
Jo
Nice shot
Unfortunately, you lost data by clipping the histogram off left. My guess would be that you lost a lot of stars around the cluster in so doing.
Best to leave all the histogram visible. Control the background by taking more frames and stacking them rather than making it black.
Concur with the vibration. A wooden deck with a long focal length is a problem.
The stars in a cluster will wash out and lose color when shot at 180s and 800 ISO. That is an exposure appropriate for a medium intensity nebula, not for stars, especially at f/6.3. Too much light