TwoSix
Everyone's literal second-favorite poster
But that's ignoring the fact that a 1st level spell cast from a 5th level slot should be inferior to a 5th level spell. Choosing a 5th level spell as a spell prepped/known already has a massive opportunity cost, in the fact that you can't use it with your level 1-4 slots. The fact that upscaling is almost always inefficient is what keeps us from the scenario where the optimal play is for casters to prep all 1st level spells, except for a few utility effects that only become present at higher levels. (And yes, I believe that is the design intent, as preparing a breadth of spells across multiple levels has been the default of every prior edition.)For scaling, scaling is supposed to make a 1st level spell be on par with, say, a 5th level spell when cast in a higher spell slot, at least for damage.
I mean, the spell I can think of right now that becomes a better option when upcast is Armor of Agathys, and considering that's a warlock spell with auto up-scaling, I also assume that's intentional.
Obviously, your game, your house rules, but your design intent cuts against what I perceive to be one of the most elegant features of 5e spell design.