Well, I wouldn't call Bale especially fragile either, more like indifferent towards the end. But I see what you mean. Still, I remember Son needing several "playing himself confident/in form" spells through the years, where his confidence looked shot. Point being, some players can fill a role and being useful because their game is more about doing things right than doing the spectacular, so to speak (Højbjerg, Skipp, Winks, even Porro as loose examples), when not on top confidence wise - while some players are better on the bench because their usefulness dips below zero when not on the money.
Again, this is a very loose comparison, and mostly for argument's sake.