mulegolf This old deck has lasted a long time though. I built it myself in 1980 and it's still pretty much level. It was built using pressure treated 2X6's. It's hard to believe it's lasted 44 years...
I found that each time I apply the paint to the deck with a roller rather than my sprayer the power washer seems to peel up the "paint" from the deck more than when I spray it on.
I built a deck in 1985 using pressure treated 2 x 6's and it still is solid and looks very good. I built another lower level deck about 10 years ago using pressure treated 5/4 boards and this one is started to rot and needs some boards changed. I am guessing the govt. banned some chemicals used to treat the original 2 x 6 lumber. I last sprayed these with an oil based semi transparent stain and trying to decide what to re-stain or paint with. I'll have to consult with "Bob" and older dude at my local Ace Hardware who runs the paint department. He is very knowledgeable and can color match stuff by eye as good as the computer gizmo does.
Regarding the sprayed paint vs. rolled it could be whether you thinned the sprayed coating first. The thinner paint (stain) will penetrate the surface better than the thicker and adhere better.