Different maps has different initial resource spawn. It is a competitive game. The starting condition should be the same. In ranked game, some maps are just good for certain civs. For example, age2 rush civ like Chinese and Lakota has great advantage at those map with far resource spawn. Mines and hunts are far away from TC. Their opponent has no way to get out and die slowly. Thanks to stupid age2 rush unit card.
Is there any balance change on the maps to make things coherent?
There isnt an inherent problem with random starts, in terms of determing someones skill it would rank them higher as they can deal with different starts. The game shouldnt be about memorizing the first 5-10 minutes so it becomes like chess. It also shouldnt be all the same layout for maps as those maps will get boring pretty fast.
As long as both players have the same start (a few trees missing arent really a problem honestly) and the sides are decently balanced I dont see the problem of variety
AoE3 is a strategy game that tends to be heavily based on your ability to adapt your strategies to what is around you - You’re tested on your ability to respond to the environment you’re thrown into as well as your understanding of your own civ as well as your enemy’s.
If every start was the same, it’d be boring. There’s a lot more RNG to this game than a lot of other RTS games. It’s what makes it exciting - Every start is different. It’s why having a slew of decks is a necessity to be good - you need to have different decks suitable for whatever resource management you’ll need, as well as several geared towards the specific situation you’re in.