Every civilization in AoE4 has unique mechanics. Some require you to manage a special resource, activate abilities at precise moments, or execute a tight sequence just to function at all. If you are still learning the game at the same time as learning that unique mechanic, you end up stuck on two learning curves at once.
The fundamentals of the game are the same across all civilizations: keep
villager production running without stopping, spend resources before they pile up,
scout to understand what the opponent is building, and fight with a purpose. A civ that forgives mistakes while you practice those fundamentals is infinitely more valuable than the best civ in the patch if it forces you to micro-manage something constantly just to survive the first five minutes.
The fundamentals you build with an accessible civ transfer directly to any other civ. The unique mechanics of a hard civ teach you none of that.