Scott mentioned Reprobation in his recent article on brewing on a budget in white, and its another example of removal that answers a problem without immediately giving it back
While we'll talk about some cards that work well with Naban, Dean of Iteration in a minute, it's also important to point out that there's a second level to Naban, Dean of Iteration that isn't present with Panharmonicon
Factions were well balanced, there were a variety of new and/or powerful cards you could open within factions, and many people of all skill levels took to it quickly since you could just jump right into a game without spending time deckbuilding
Cards with printing errors like holographic bleed, original WOTC-era sets, and Japanese promos tend to command the highest premiums
Turning this Arena into a flying Bird that doesn't need to tap when it attacks feels too good not to add to those lists
An encyclopedia of Magic would feel incomplete without some of the most foundational and widely played cards in the games history