Frankly, if you're not a min-maxer, it's nothing really to care about. Just overload your soldier with more than a grenade-worth weight, and strength growths steadily, I mean mission after mission.
For instance, give a medikit to nearly everyone.
Now, I shall confess that I don't need really TUs efficient scouts and shock troops either (being a save-loader)...
Perhaps, the wiki should tell that, providing such a weight management, you are assured to gain strength on each mission, and that at a given strength value, you are able to wear nano-armour plus a heavy weapon, and that at another given strength value, it's power armour, etc. Just to reassure the player that its game is not spoiled because he forgot to overload two soldiers during three missions.