MonkeezOnFire
Adventurer
Creating a spell for each level could be possible but I think the designers thought that would be too abstract. I recall that during the initial 5e playtests that they received negative feedback the first time they introduced the concept of replacing summon spells with generic stat blocks. People really wanted the 3e style of using the monster manual stat blocks so thats what they went with. The current iteration might be a bit of a compromise so as to not go too generic to avoid that kind of backlash.It's not bad having options, and there's nothing fundamentally wrong with the basic mechanics, but these spells seem like a whole lot of words for not a lot of content. Wouldn't one spell each for levels 2-6 have sufficed? Or even fewer?
And I really think the flavor argument is a strong one. If we were just given generic scaling stat blocks with a list of possible abilities to choose from then you could probably create some stretched creations lorewise that are mechanically powerful. This way they can create blocks that feel appropriate for each creature type and dish those out to classes as appropriate (though I think giving wizards summon fey is a bit of a headscratcher).