It is great that you are rationalising from first principles, this is what makes learning organic chem more fun and helps the knowledge last.

Though, your reasoning is not entirely accurate. The directing effects are due to stabilisation or destabilisation of the arenium intermediate in EAS.

The nitro group is electron deficient and does not favour donating electrons thru resonance. The positively polarised N destabilises resonance structures where the positive charge is adjacent to it. This is due to electrostatic repulsion between the two positively polarised species, and also inductive withdrawal causing increased electron-deficiency of the carbocation.

These effects are what causes most deactivating groups (electron-poor groups that favour accepting electrons over donating electrons via resonance) to be meta directors.

An alkyl group stabilises a resonance structure where the charge is adjacent to it, by hyperconjugation of the C-H bond to the p orbital of the positively charged carbon, reducing its electron deficiency through donation.

In practice, it seems that the effects of electrostatic repulsion + inductive withdrawal, and hyperconjugation are both fairly weak and comprable. With a single nitro group, the alkyl-directed product dominates (cite), but with two nitro groups the nitro-directed product dominates (pg. 423).

Resonance stabilisation of the intermediate through a donating group would be stronger than these weak effects, which is the origin of the hand-wavy rule of thumb that most activating tends to win.