Direct Hit is just diet Crit
No sane player builds it over Critical hit. Why should the meta be so rigid? Why not make DH affect proc rate? For proc focused builds starting out with a base percentage is great, but why leave it a fixed percentage when DH could easily contribute to strategic variety by affecting the rate at which a skill procs an effect? An added 25% damage every so often is redundant and could be funneled back into crit and rebalanced.
If the tier bonus is balanced to always be an additive percentage of a skill's base chance, then it could give players more incentive to stack Direct Hit. That way the gear stat curve also doesn't neglect an aspect of the kit as the stats rocket upwards in later content.