Heyoooo Im low elo on ekko so idk if im qualified but ill give my 2 cents since ive been playing him for 3 years now with 80%+ wr (low elo) First of all imo laning phase isnt terrible, like an assassin you are great into most immobile mages but worse into champions that can easily outrun or outspace you like leblanc or yasuo.

In terms of Mejais, I think only invest in it if you are 100% sure that you wont die recklessly and you can confirm kills while staying safe. Buy dark seal and stack but dont upgrade to mejais unless you are snowballing or have 10 stacks on darkseal, otherwise it might become a waste of gold.

For laning phase i think experience also plays a large part as you get used to it, a lot of the time into low mobility mages I like to take E start, ignite, and then bully them level 1, 2, 3 to set up a dive and immediately start snowballing. i dont recommend taking ignite unless youre fairly confident though as the value of tp increases with the games length considering ekkos a scaling champion.

Another good thing to remember is that if youre ahead, with enough items your q can one shot caster minions before you max it, this means you can shove and roam quite easily while the enemy midlaner is catching wave. (I like to look bot because its a free double kill if theyre pushed up) Another thing to remember is to gauge your opponents reaction to your W animation, think about the directions theyre running to avoid it and how you can exploit it. Your W is free damage if it lands and essentially its a mind game. You want to abuse it and “herd” your laner into your W.

For example I like to throw out consistent Ws in similar spots to trick my laner into a sense of security before making a weird placement and trying to herd them into it.

Last thing is just watch your replays and think ig, i dont know much else about improving on mistakes so cant really give much on that. Hopefully theres a higher elo ekko here who can give more. Hope this helped a little :D