Is dropping the cliff on duel gap an exploit?

I've recently heard of a player who got banned for a few months from dropping the cliff on duel gap because as some artillery cannot arc high enough to hit the firebase the moderator considered it an exploit.

The supposed reasoning does not fit anything in this list. So I am wondering if the list needs updating or the original reasoning was erroneous or I heard wrong.

Simply looking for clarification and/or a concensus.

No its not

My personal opinion is that it is a map issue.
Similar problem was with old versions of badlands.
Fixing arty to make it able to shoot up hill so high might be not easy (surely harder than fixing the map) and can cause other unexpected problems.
options that i see:

1. treat it as a map feature, just deal with it, abuse it and don't let enemy do the same
2. Lower highground so arty can shoot upthere
3. remove landable and buildable area
4. gentleman agreemen to not build anything there (kinda like "no hill" on the thermo)
5. maybe can try to make a mod that makes arty shoot up on high hills, if there will be no problems with that mod then maybe those changes can be added to FAF (or maybe not, can't promise here)

6. Add a ramp so people can send a land army up there from the low ground

There is a similar problem on Cobalt Valley. You can drop light arty onto the plateau and cause problems, it's not easy to get rid of them. If there was a ramp inside the base, people could walk up and clean it easily.

it's map's issue,not an exploit,you can find the exploit list here https://forum.faforever.com/topic/203/list-of-banned-exploits-updated-02-06-2021