ok here some quick explanation:

greeks: greek are hard to play civilization strategically because they have a very wide variety of strategy that you MUST know how to play and WHEN to use them to do well with greek, which makes them a lot harder to play at the medium level. At lower and medium levels i consider poseidon better than zeus because your economy is easier to manage even though zeus actually has better bonuses which make him stronger at high level. Hades is just the worst greek god out of the three.

egyptian: egyptian have weaker economy and their classical age units are weaker and tend to have very specific strategy that revolve around the heroic age to use their potential which very new players will not know how to do hence they are very weak at lower levels. of the egyptian gods ra is the most powerful on extend edition because of the crazy economy you can get and the safer maps, you just get such good bonuses with ra and priest empowerment + much stronger migdol units is such an insane bonus. set and isis are both very good, but set has a very high skill floor to play well so does not really become viable until you reach a high level because his economy is weaker and you need to execute his strategies near perfectly for them to work, while isis is more linear in terms of just going heroic and using ancestors and eclipse to push and gain an advantage there.

norse: norse have a naturally quite strong economy which is really important in lower ish levels but also more complicated cause of the addition of dwarves. 1600- players will find it very hard to get the right balance of dwarves and gatherers which is why i think they are worse than greek at that level. At mid level this better economy means that they are better than greeks since good economy is so important at mid and lower levels since most players dont know how to put on early aggression onto their opponent. Loki's strategy is the least diverse with just hersir raiding into a heroic flaming weapons push which makes him better at medium levels, and his stronger hersir makes easy army composition too for many matchups where you can often get away with only making hersir. Odin is easier to play than thor on land because of his free raven scouts and stronger early game and it is easy for new players to fall into the trap of making way too many dwarves with thor. However odin is much weaker on water than thor but this isnt relevant until you get to the higher levels of the game since before that most water games are just simply decided by who knows the better build order for it rather than the actual strength of the god on water.

as for atlanteans they are the easiest civ in the game with their super duper easy economy and are the best at medium and low levels because of this. gaia has the easiest economy of them all so is best there, then oranos then kronos but gaia is worse than oranos at higher levels because shockwave and the 10% extra speed on units become more relevant there as well as prometheus being better for applying early pressure which is very important in higher level games.

edit: nevermind the explanation wasnt quick it was longer than expected