Nuketown's unique properties significantly skew the average XP and related earn rates. A Nuketown only map playlist running all the time is destructive to the game's progression systems.
First of all, this makes the incorrect assumption that BO3's progression system is worth preserving when not only has it not improved on anything it's gotten worse by excluding features introduced by the previous three COD titles.
Second of all, this ignores an entire field of mathematics available to your team to improve the system. You could easily take into account Nuketown's alleged statistical skew and adjust its numbers accordingly. Here, let me write up the fundamentals:
Have two factors, "Map Factor - Deathmatch" and "Map Factor - Objective." In fact, you could split it into a separate Map Factor for every single game mode if you'd like.
For both factors, put together a stat called "Weighted Time-To-Die". With what frequency and in how great of numbers are players dying in a given game mode? Establish a baseline Map Average. Call it "Weighted Deaths Created." Determine the average, determine what maps create less deaths, what maps create more. Identify how much of a skew, if any, is present on Nuketown.
Attenuate and/or adjust Nuketown XP gains and Nuketown KDR. If players gain 20% more XP on Nuketown than they do on any other map, lower XP gains by 20% while playing on Nuketown. If players are killing each other 20% faster or 20% more on Nuketown than any other map, lower the KDA weight for Nuketown by 20%.
I could work out the math for the system for you right now if I had the full numbers, and don't tell me this shit isn't feasible because all this is just baseball sabermetrics as applied COD and you already have the numbers, just not the codified statistics.
LASTLY, the reason I want to play Nuketown is because all the other maps are categorically terrible. I kept wondering why, and eventually I realized the answer was that all the advanced movement was tacked on. All the special movement, the Aerial Movement and Wallrunning, was shoehorned in at the last minute because Exo movement was so popular in Advanced Warfare that Activision told you guys BO3 had to have special movement. I find it impossible to believe that a team that knows vertical movement will be a heavy part of the gameplay would design Redwood. It's just not possible. I feel for you guys for having that thrust upon you, really, but that doesn't justify overly curt responses and it definitely doesn't justify easily solved alleged issues of map balance.
That said, if the DLC rolls out maps that properly utilize aerial movement and verticality, I have high hopes for the game. And Zombies is great.