Not necessary... i tried training with friendlies and normal training. Found friendlies will get your players more tired but award a little gain of skills.

Better train with coaches. My current regime so far with certain set of training regime giving me +1 level up for every 5green packs... average i spent 100 greens to upgrade for 20 level per players. For every 100 packs i can upgrade a 5* into 6* players and so forth...

With friendlies i get less. So it is not true friendlies giving u advantage than training with coaches...

Its better focus which players u want to upgrade and not all. With training coaches u can achieve this.