I think random maps with default resources require a lot more skill than death matches. Every move needs to be calculated in RM to build a strong econ then strong military. RM utilizes strats and skills through every age. You must know what technologies and units to use through the ages, and when to advance through the ages.
Random maps offer SOOOOO many opportunities to differ from your opponent. How many villas do you make in Stone? Do you have an army in Tool? How do you defend a Tool attack? When do you start mining gold? Do you mine stone? Can you afford the loss of food and wood if you do mine gold or stone?
What is your Bronze time? How strong is your economy upon entering Bronze? Do you attack with CA's or Compies? Do you have a big Bronze army or use the resources to go to Iron? How much more did you grow your economy through the Bronze age? Do you research nobility first and attack, or research shared maps and look at the field from a team perspective?
Once in Iron, what "super unit" will you get first? How big is your economy compared to your opponents? How are you going to stop/prevent opponents from flooding your land with Scythe?
These are all aspects of every game and then most aspects of DM's come out in post-Iron random map games. Each team has huge economies feeding huge armies.
I am not saying that in a DM there is no skill. I have played plenty of DM's and I know there are lots of strats/skills needed to win.
My overall opinion is that there is a lot more excitement in balancing a fragile economy, utilizing scouting/forward building, and building Tool/Bronze armies. Winning an RM is a lot more satisfying to me than winning a DM.
My DM building pattern is always just get all of my resources out on the battlefield as soon as possible and have a large group of villas gather resources to maintain booming ele's, cats, and towers once the original stockpile is used up.