Black is well positioned though to remove blockers and a 5/5 does a lot of damage on a clear board (and even without a clear board, it costs your opponent a blocker each turn).
I think people exaggerate to some extent how obsolete older creatures are. Sure, Juzam is not above curve anymore but you could slot it in a lot of decks and the card would be good and win games still. Magic hasn't changed that much. Most of this has been incremental. There are a plethora of creatures still good enough for cube that people just shine on because it hasn't been in a list in years (or ever).
Erhnam Djinn is still good for example. Wasn't until my retro experiment that it struck me. 5 toughness is a lot (survives wildfire) and it's splashable, so sweet as a filler pick in any Xg midrange/aggro deck. Polukranos is more powerful, but that GG in the casting cost is an actual cost.
Just the other day I was watching a cube draft with I think a ChannelFireball person and their opponent played a morphed
Exalted Angel and they proceeded to mock the card only to lose that game to it.