The lifegain mode is, again, niche, but slotting in a repeatable lifegain trigger into a deck like Lathiel or Krav & Regna is really not the worst, especially given the kinds of spells youll have protection from
These tokens can be used to bank mana for later, when Daretti can't attack safely, or sacrificed to bring more important artifacts into play from your graveyard
It gets better, because The Ur-Dragon draws you cards whenever a dragon you control attacks and then lets you put a permanent on the battlefield from your hand
These creatures typically cost 4 mana, so 3 is a meaningful discount, plus you get cost reduction for other creatures
It's like they went back in time, and no other MTG card would dare try something like that.