in addition to the above:
You go for the whole Market Garden approach..that's impressive.
But realize you make this CCgame primarily for more than 2 players.
And to have a map with all too fixed /rigid map patterns (decay at many places...only a thin stretch of road being hunted after by all players) and a concept for really only two adversaries (drop point allies, drop point axis) could hamper this map to a dull game after a couple of plays.
Like you said the risk is that the players in the axis drop zone fight it out first amongst themselves..and the same for the allied players.
You must make it interesting/worthwhile for each of the 8 players to find an individual path to win the map.
The previously mentioned Airsuperiority chart adds to that effect.
Thus I am not in favour of decay hexes for merely difficult terrain (after all..your troops don't die because of ploughing through a marsh). The only effect marshes, off road and on-road can have in a CCmap is speed/reach.
Fast moveable hexes (roads) should be linked together to one field/territory.
So, marsh/wood = 1 hex = 1 territory
Field, Grass, cultivation, city = 2 hex = 1 territory
Road = 3 hex (in line) = 1 territory.
You could place the airsuperiority chart smack in the middle between the Legs of the "C" map.
Driel------Arnhem --- Oosterbeek--deelen
I .........................^
Nijmegen (Air Superiority Chart )
I....v.....................V
Groesbeek --- Grave --Veghel--Eindhoven
And instead of an Air Superiority chart (paradrops, control over skies, bombers, Flak hits) you can enlarge that concept to supply/support dominance Chart (paradrops, control over skies AND supply, Panzers from Germany/repair stations, bombers, flakhits, artillery hits on supply lines).
A sort of "über"control body concept ; the more you gain in this chart the more you are able to drop paras at certain maplocations (Oosterbeek, Groesbeek, Veghel) , the more you can pour panzer reinforcements in Arnhem/Groesbeek area, the more you can move 30th Crps troops into Eindhoven, the more you can Ju88 bombard certain maplocations, the more you can artillery barrage bombard certain road hexes..
Annd from the groundmap going INTO the Support Superiority Chart via;
Airstrips (control = fighter airplanes), Flak and AA hexes (bombard to neutral certain Sup Chart hexes).
All this makes it more fluid, and each of the 8 players should be able to control a certain area of the gameboard and be able to conquer the map with a fairly equal chance of succes.
Barbarus hic ego sum, quia non intellegor ulli.