I dont think playing only one map should be something for ranked but instead for unranked.
You ranked elo should show how good of a Player you are, and if you are a one Trick Pony then you should be punished for this by losing on other Maps.
After all Ranked is the competetive Game mode that is designed to show the skill of each Player, which is why any Competetive RTS Game has a Map Pool. The Map Pool forces the Player to be adaptable and be skilled over all, not just at one specific thing. I also could have a higher Elo if i only play Hideout and islands, but this would be fake elo then.
In the same way I knew people who only played one map, dodged all others and pushed their elo this way, despite being worse then their shown elo.
Its not a problem, its more a design question:
What do you want Ranked to be?
Should it be a mode that is designed to show the skill of a player, or only a matchmaking system to find fast evenly balanced Matches.
I think most players would want Ranked to be a competetive mode that mirrors the Skill of the Player, which means you have to play different maps. (Tbh i already disliked that they added the function to favour maps because it makes it possible to nearly only play Arabia or Arena)
But I agree that there is a Playerbase that doesnt want to play multiply Maps and still want a fast Matchmaking system to Play this map.
My suggestion: Edit quick play:
Give quick play a different hidden elo (a hidden elo basicly works like ranked that isnt showen but used for match making) and then the option of infinity Bans.
Ofc the more Bans a Player uses the longer he has to wait for a Game (because the system needs to find Players of similar hidden elo that didnt ban this one single Map), but its the decision of the Player to take. If one wants to wait longer for the specific map they should be able to in quick play.
This way Player could only play the map they want with a matchmaking system without making Ranked less competetive.
But as you have seen in my Post above i also think Players have different Playstyles and strengths which is why the Ranked map pool should be diverse with maps of different styles, and not as one sided as it often is nowadays with mainly open maps in it.