I disagree, cosmetics and mounts from chests shall remain a luck factor. We have pvp coins shop for cosmetics and mounts that you can grind. People already don't grind for the pvp coins shop stuff, what makes you think they will for the ones from chests ?
We can have "guaranteed" something by balancing the rates and rewards. As I mentionned earlier, the main issue is having useless TMs that are destined to rot in bag.
Although I kinda agree with the fact I don't understand why all news ways of getting rerolls are always soul-bond rerolls that cannot be used with double reroll thing.... i mean... why...?!!!!