Hellholt Engineer is rated 4.24 on agotcards.org today. I can't tell if a bunch of people rated him a 5 after Worlds, but the newest comments are over 3 months old. Feels like a high rating for a virtually unplayable card.
You really can't go off of a rating on agotcards (or anything else) for playability. Most of the ratings are made after the card is spoiled, but before it is released and anyone has actually played with it. And the environments change. Fox's Teeth is rated as 4.27. The Wildling Horde is rated at 4.38. So they must be even more
"playable" than Hellholt Engineer, right? But they don't make the general cut too often, either.Ratings tend to reflect the "wow" factor of reading the card, not the card's general utility or playability.
That said, every card is playable in some build. I'm not saying Hellholt Engineer is bad card. In the right deck, he is a "money card." All I'm saying is that because he is a 2-STR Ally, he does not make the cut in most decks that are not specifically built around using or abusing him. Martell players, in general, choose other 2-STR characters (Ally or not) in decks that do not center around certain location effects.
Ultimately, the "should there be a blanket 3x per phase limit" is not a question about whether or not certain character abilities should be allowed; it is whether or not certain deck types should be allowed.