Pom's problem isn't the velocity. The FB velo is dipping, but so are the rest of his pitches. If they were all converging to the same speed, it'd be an issue.
His problem is that his curveball has been an absolute mess (-10 runs above average). It used to be one of his trademark pitches, but it's just not working right now as he can no longer locate it and is leaving it up in the zone. He's never generated much swing and miss on that pitch, so when he leaves it up it's getting hammered.
The BABIP on his fastball is only 211, for his curveball it's 469.
The sinker that he throws isn't great and generates a lot of fly balls so it isn't good enough for him to be a two pitch pitcher. He needs to figure out that curve. If he can't, he becomes a DFA candidate IMO.