Warriors don't really help your Engine run...If the Warriors are contested, you may only get 2-3 of them. Hardly enough for a draw engine.
Well, they certainly help more than Treasure Hunters or Heroes! +2 cards is better than 0 (actually, -1 since they both gain treasure!) The point is, if you buy multiple Pages, upgrade one to Champ and the rest to Warrior, whatever that number is.
Sure, you could buy only one Page, planning on playing Champion + lots of terminal draw cards that are better than the +2 from Warrior, but if your opponent is buying Pages, you had better hope their Warrior doesn't hit your Treasure Hunter or Warrior or your game is completely over. Better to have a little bit of insurance that turns into a Lab than be dead in the water.
Are there other things you can do with the Page path? Sure, there are always edge cases. Treasure hunter/Feodum might be a thing, except for Warriors trashing...um...everything in your deck. Hero/Remodel might be a thing to gain Gold/Platinum and remodel to Province/Colony. But I submit that Champ/leftover Warriors should be the most common way to play this path barring something unusual.
I'm not buying the idea of upgrading all of the leftovers to Heroes. Sure, you can gain a lot of platinum, but even a hand of 4 platinum only buys one Colony, barring a Workshop/Nomad Camp/Messenger in the same hand, and if you're playing a bunch of Travellers too, should your luckiest possible hand be a hand with none of them in it? One Platinum is enough to buy a Colony a turn with halfway decent draw. If you want multiple buys, you need a reliable draw engine, not more big money.
One more thing: As great as Champ is with terminal draw, it's a delicate balancing act. You can't exactly buy four Smithies and just wait around for your Champ.