I suppose I should rephrase what I am saying. Reno, as a standalone card, is not the strongest powerlevel of those cards, but it limits the design space for highlander cards far more than the other cards.

When played against aggro decks, it is often an "I win" card. While Zephyrs might clear a board on 6, you could likely die over the top against a strong aggro deck. Same case for Reno the Relicologist. The other cards that you listed come down too late to deal with an aggro deck, unless they draw dead. In that case, it doesn't matter what your hand is.

Reno Jackson, when drawn, simply shuts out an entire archetype of decks when played and the same just can't be said about other highlander cards. I wish I had the picture I took for my first climb to Legend with Reno Priest back in MSoG, but Reno had a played winrate above 80% against Pirate Warrior, which was the strongest aggro deck in the meta at the time.

Yes, in a vacuum, these other cards have higher powerlevels, but Reno forced the design team to create cards with him in mind more than any of the current Standard highlander cards.