I don't get complaints about Champion's infinite actions at all. It must just be a perceptual thing. There were people saying that a card could never cost $7, because that would break the game, as if 1) that card would be in every game from that point on, 2) you would always want it when you could have it, 3) when you did get to buy it the game would actually be worse. It's the same here. Page isn't in every game, in fact you almost never see it. When you do have it you don't just start the game with Champion in your deck. Once you have that Champion you don't just naturally have a deck full of terminals. You put work into getting Champion before the game ends, into having your deck function before you get it and yet having it pay off once you've got it.
And really. In Dominion, you can play one action on your turn, except, and then buy one card, except, and then discard everything, except, and draw a new hand of five, except. Treasures just make money, except, victory cards are dead, except. There's the cost in the corner, except, and the types on the bottom, except. You open with 3/4 or 4/3 or 2/5 or 5/2; the trash has cards that are out of the game now; there are 10 kingdom cards and 7 base cards; your deck starts out with 7 coppers and 3 estates.
Over and over I tried to find anything left that there was no exception for, and made the exception. You can't just make one game into every game, because you have a particular audience and there's what they like. There are no Dominion cards that require anagramming, for example. In the 90s I sometimes tried to stretch games that far, here now it turns into Scrabble, and well it's no good, you want to find a core to rally around, and then deviate from that while staying in the area. Anyway Champion fits neatly into the framework of Dominion, it is not anagramming. And I've played with it plenty and it's pretty sweet.
Now Warrior, I can understand complaining about how demoralizing it is to lose your Warrior to someone else's Warrior. It was not overlooked, it was discussed, it was a real concern. In the end most playtesters did not mind it and as you know I let it happen. Get more than one Page, that's my advice. Get cards that cycle through your deck faster, like Dungeon; Warrior can't kill your Hero, although it also hurts to not get to upgrade that shuffle. You may wish to avoid playing with Knights and Page/Peasant in the same game; every Knight attack is so terrifying.