Leveling up special skill unfair

About Mathematical approach is on debate.

This graph, mention that 10x at a time and 1 at a time is same.
https://docs.google.com/spreadsheets/d/1xidazrIQYdpHWK63GHcEqOB_MWAoQhQ9JEscdk6t_6o/edit?usp=sharing

Now, thats make sense with this exception, thought thats way around 1-5 heroes at a time is still more or less or have same chance, because it is still RNG. And I still leveling *3, so I do not want use *2 to my *4 heroes, until maybe at tier 4, because it mostly more food costs, so then my development at that time (if all *4 are at 3.60) then I stop leveling *3 (almost done). So next *2 feed not for *3 heores instead for *4 heroes tier 4. And continue *1 heroes for new *4 heroes Tier 1.

So conclution for me, for stoburn hero that di not skillup doing 10x at a time, I feed around 1-5 heroes at a time until 8/8.