Yep, it is indeed powerful - but I think it is exaggerated here vs TT - you have limited smites, and you need a long rest to get them back. A DM can simply send you into a string of encounters where you need to manage your spell slots better, not you get them back per combat. Also, in the example, the hold may have failed - so that was just good luck.
What is more broken is haste giving a full +1 action. It would be easy to fix it - but they chose not to. Try swap the paladin for a *hasted* paladin at level 5 + PM. If you have the slots, and you hit - that's at least 5 attacks in one round including the 2* 2 attacks + 1 bonus attack, each of which can smite. And that's before shenanigans with multiclassing. I guess in 5e they assumed in a well paced campaign you'd couldn't rest wherever. I don't see the bonus attack as being an issue though - if you dual wield, you could do that anyway (sure not as much as a polearm, but you can take a feat to wield to non-heavy weapons).
