That’s hardly evidence. “they usually get unbanned” … who are “they”? How many? And “one guy” is not evidence of anything.
First, the examples might be just a small fraction of the bans handed out. Really, without some idea of the number, out of the total number of bans, it’s impossible to draw any conclusion.
Second as DECA AFAIK don’t publish reports, this must be from players who choose to report their success appealing. I doubt they are representative.
Third: I am sure DECA would be criticised if they handed out too many bans or too few. In fact I’ve read far more complaints about bans from players than reports of their success appealing. It could be they are striking a balance.
And Fourth: as with people complaining about “unjust” bans there are always two sides to any story. We don’t get to see the evidence DECA has of any ban, we only see what the player caught cheating chooses to report, which can be incomplete, exaggerated or just plain inaccurate.