Scaling only goes so far, so no, eventually you will get to a point where you’ll be able to just blast things even though those same things are your level.
I mean, just look at Diablo 3 as a perfect example. Everything in that game scaled up with you. At level 80 the Butcher was still a boss for you the same as it was at level 20, and as you went up through the Torment levels he got tougher and tougher. But as you got better armor, item bonuses with unique effects and massive damage multipliers, you could swing back in and melt him in one or two hits.
It will be the same with Diablo 4. You’ll easily get to a point, gear wise, where you just melt anything that looks at you funny.
Hell, it’s even possible right now to melt things with the right build. Necro bone spear builds can melt bosses and regular enemies extremely quickly with a few crits.