A couple quibbles on my part.
Gaines is in year 3, is OG4, has no proven position flexibility at the NFL level, and has played 22 snaps over the past 2 seasons. I don't believe this resume constitutes a "good" player.
Jones is currently playing behind two rookies in Will Johnson and Denzel Burke, and in battles with Kei'Trel Clark (3rd year, fringe roster) and Darren Hall (4th year vet) for the 5th CB spot. Jones SHOULD be able to win this spot as the competition is weak.
I don't know what good players on the defensive line will be cut. Maybe you are referencing Jones and Nichols. But then, people on here argue that they suck so I don't know that they qualify either even if I disagree.
Your best argument is if Kitan Crawford or Joey Blount get cut but I don't believe either will.