Is that not the point of the rules lite? It fits within the theme and intent of the ability, after all. Or are you going to say that an evoker can't avoid destroying a wall with thieir fireball, but manage to avoid hitting a bag of rats in the dead center of the blast?
I would rule that the evoker could allow up to four of the rats, assuming a third-level fireball, to automatically pass their saves and take no damage from the spell. Since there is no mention in the feature of objects, and since the rules on damaging objects make no mention of saving throws, and since the idea of a wall succeeding on a dexterity save strikes me as incongruous, I would say that the objects have failed their saves before the spell is even cast. Even the rats that survived the spell would still be in a flaming bag.
Of course, house rule as you like, but be clear that you are doing so.
Now, as for ratings . . .
Arcane ward - 8/10 - Has benefits in combat and exploration, encourages you to cast spells of the related school, and helps you maintain concentration. This is about the best there is.
Minor conjuration - 5/10 - A Swiss army knife with applications primarily in exploration and as a spell component, best for its unlimited uses. Somewhat limited by DM discretion.
Portent - 6/10 - Has functions in any of the three gameplay pillars, but the randomness reduces its applicability. If you roll in the 9-12 range, it can be like not having a feature at all.
Hypnotic gaze - 4/10 - Modest uses in all three pillars, but too limited for everyday use.
Sculpt spells - 6/10 - Powerful when it applies, and it sort of encourages you to cast spells of the school. However, it has no use outside of combat and even in combat only works in specific circumstances.
Improved minor illusion - 5/10 - Gaining a cantrip is always going to be good, has value in combat and social pillars, maybe a few uses in exploration as well. Rewards creative play, but in the end, it only improves a single cantrip.
Grim harvest - 2/10 - Only good in combat, requires that you strike the killing blow with a spell of first-level or higher, scales poorly, and doesn't do anything if you aren't taking damage.
Minor alchemy - 2/10 - As far as I can tell, its primary uses lie in ripping off shopkeepers and bribing low-level mooks, and it creates more concentration saves.
Bladesong - 4/10 - Powerful for a certain combat style, with the very rare application in exploration. Except for two minutes per rest, it's as good as having no feature at all.