Yes, that's true. There might be ways to "break" the spirit of the format, but let's face it: Your transmute/Junktroller scenario would be just as true even with a typical 60 card/4 copy deck.
So even though this format is "breakable," is that a good enough reason to abandon it entirely? That's more or less the question I'd like feedback to.
Also, time shifted cards. Do they count as the rarity they were originally printed as?
That's a GREAT question. I certainly don't have all the original rarities memorized, so perhaps that's yet another reason to institute the "rarest rarity takes precedent" rule, as another poster mentioned. In this case, the purple symbol would qualify timeshifted cards as rares.