Sure. Everyone is free to disagree and do the same calculations I did replacing 10% with whatever number they see fit and draw their own conclusions. Regretfully, most people are not interested in doing that.
If you think that a level 7 coach will train your players 20% or 50% faster, by all means, go dump all your savings in getting one. I picked the first number I thought of, which would have been on the high end of what I would have used, were I designing the system.
"I don't know half of you half as well as I should like; and I like less than half of you half as well as you deserve."