Thank fucking god
This is problematic. How does this solve anything? I'm assuming the issue here is that Ruin is very rarely practiced and played in tournaments, but what makes you think that dp4 will be any better? As far as I can tell, there has been no community vote, no real testing of the map apart from the extremely short ammo remix testing, and it seems like it's just a hastily made decision. What even happened to the mapping tournament that was planned during the first months? It's not like Ruin is a bad map either, it's just not played because only a few people from the main regions play it. Just look at the aussie boys, they seem to play nothing but Ruin.
The issue with this decision is that you already fixed the problem: the map picking system. If you want people to practice the least played map in the pool, then just have people pick first instead of banning. If a player doesn't practice a map, then they risk having their opponent pick the said map on their first pick. If the map still doesn't get picked after that change, then feel free to ditch it out.
If you just want more variety to the map pool, then don't keep the maps that have been played 24/7 for years now. Regardless of what you do to the other maps, people will always favour the usual trio of t7/t2/thcdm13.