Skill speed doesn't affect auto-attack speed, only potency. If it affected the speed, it'd be the best meld for more sheltron uptime.

Det/Tenacity- I just don't see them having enough of an effect to be valuable at this point. Should survival become a melding need, that would change.

I myself am melding direct hit simply because it doesn't come natively on tanking gear and has the biggest dps impact.