That's kinda false.What made 4E a pain in the posterior at high levels was that a single turn could take an hour. When every action can trigger a reaction, when there are dozens of conditions you have to track, when every power is unique and needs to be reviewed because some things were open to interpretation .... nope. D&D 4E was not easier to run or play once you got past heroic tier. Not in any game I've ever played and I ran and played in 4E up to 30th
Most of the classes have straight damage or healing powers or power with little to track.
The best defenders just attack attack attack mark.
The best striker is the ranger that just attacks at lot.
But nooooooooo
Everyone wants to pick the stuff that grows thorns, and creates zones and inflict 3 different conditions.
D&D fans mostly either pick the complex stuff or force TSR/WOTC/3PPs to include complex stuff.
The guy who just chucks fireballs or firebolts depending on the number of foes justs their character fast and has fast turn.
But nooooooooo
People have to take all the weird stuff or complex stuff that all use different rules you have to look up of analyze constantly. Then complain that the turns are long. This happens in every edition
So went you start at high level, your PCs and monsters are filled with complex stuff and it become too complex to learn or play quickly.
A noticeable amount of the community want to have aspects in the game which keep them from playing the game.