If they draw, say, an Advocate of their own, the Rallier is just going to be a speedbump on its way to smashing your face in
When played on Turn 5, it will draw only a single card per hit (though, like Dragonlord Ojutai, it kills remarkably quickly), but in the late game, this dragon can gas back up the Blue player
She is at worst a two in one card and at best a massive dangerous threat that you have to be most careful about how you deal with her
The strategy of a Trostani deck is pretty straightforward: ramp up quickly, create lots of creature tokens while playing big creatures, and lean into lifegain synergies
At best, I could see Harold as a sideboard card to punish control decks that tap out for a sweeper or threat, but the original dream of one-shot people out of nowhere was getting further and further away even as the list improved