Yes, it will work, but you won’t be able to see the stats provided by an item that way.
You can more easily accomplish your objective by unchecking the “use item stats” parameter found along the top of PrimalItem BPs. Unfortunately, it also hides things like armor or hyperthermal insulation from view (even though they still appear to be working). You will only be able to see the durability bar (thanks to “use item durability”), but not any numbers.
In any case, that’s still around 80 items you’d have to replace - 30 armor pieces, 28 saddles and some number of tools/weapons (don’t recall the amount).
The explanation on quality definitions is given below the formulas. It’s a derivative that controls how items are displayed: prefix such as “primitive”, name text color - and XP multipliers. It does not control the generation of items whatsoever.
Changing the threshold to the same amount for multiple definitions may cause weird behavior and even crashes.
Emptying the list altogether will likely cause crashes.
Leaving only one definition will only make the game display all items as the same quality (and provide the same XP multipliers), it will not affect how stats are calculated.