Or as others have said, embrace them. Always restricting or strain them is not necessarily good/fun design either.
Also, it is not like I need tier 5 (which does exist in 5e) to challenge tier 4 adventurers. I find that assumption flawed.
I think you are confusing things.
There's
Dungeon Adventure and
NonDungeon Adventure.
Dungeon Adventure is about resource management.
Dungeons are about traveling through X number of enclosed encounter at the party's pace within an adventuring day.
NonDungeon Adventure does not have to be this.
If you want to do a
Dungeon Adventure, you need features stronger than the party to hold them between the bounds and walls of the
dungeon to drain their resources.
As PC level, they becomes stronger and slicker. So you need tougher stuff to brace the walls and force them to stay on a path within the drain of the
dungeon. Usually these stuff are of higher tier. Thicker walls. Tougher locks. Richer factions. Stronger and Smart Monsters.
The idea behind the Tucker's Kobolds or the Mighty orc tribe is that the mnsters have the resources, allies, or upgraded leaders to make cheesing them with low level magic harder. They beat your Tier 1 magic with Tier 2 tech, wealth, and diplomacy.
The same applies to Tier 4.
If you are
not doing a dungeon, you don't need the higher tier stuff.