Yes and no.
Previously, you would lose power only relatively speaking. The entry zone would be super easy because you over-geared it and each subsequent zone would be relatively harder as you lost your advantage.
Now, with mob scaling only out since Legion, you lose real power as you ding. The exact same mob type that you just fought before you dinged is now harder afterwards. You are right that it is exacerbated for players starting out with previous expansion end-game gear though ... because while normal plays see the drop at the ding, they'll eventually make up for it with higher ilvl rewards and drops, the raider just keeps seeing drop-offs each ding without being to upgrade much at all until late in the leveling cycle.