[chii]

May be the measure should be how harmful it is to continue?

For an MMO, you're engaged socially (presumably in a guild, rather than soloing). In a mobile grind game, you spend hours constantly checking on progress for that endorphine hit.

[rizzin]

Same as with any addictive thing, you can use and you can abuse. And the change isn't instant.

You can play MMO socially in a guild, or you can simply grind max levels / rare items endlessly.

You can play an IAP and ad-riddled mobile game to kill some time when waiting in queues, or you can have it become a part of your life checking the game everytime you have a minute of downtime.

And the transitions between those states happen impreceptibly, and there is no defined line beyond which you may consider the activity harmful.