When you make a mechanic that rewards a player for not doing something, it's usually bad because it has weird implications. In this case, try the opposite. Reward the player for having a creature with least power.

Think about it thoroughly. If you control the biggest creature, all your dauntless abilities are simply dead unless your opponent decides to best you, which he/she can now use strategically instead of you. In fact, you'll have to make horrible decisions, like deciding whether to play your 3/3 so that you can actually have some board presence because you're 1/1s aren't helping, but at the cost of nullifying what your cards do. And if you decide wrong, you could be scrambling for answers for your own 3/3. Your optimal dauntless deck would be a bunch of weak creatures. So your curve would suffer. You can offset this a bit by designing weak creatures with relevant creatures at various CMCs, but that's taking too much space just for this. And every cool big creature you might want will go against your other cards. Mechanics that make you fight yourself are not fun because you already have an opponent to defeat.

The other way around is much better, though. You'll play weak creatures (offensive if you're an aggro deck, maybe Avacyn's Pilgrim in a midrange deck, or Augur of Bolas in a control deck), but the rest of your deck will still have plenty of options. You can go for a token making deck that includes Regal Force or Wayfaring Temple and not feel bad about it, for example. You will not be afraid to play bigger creatures because they will never make your abilities worse. The only thing that would make them worse would be to have your little guys killed or if you're opponent played a Wall (which you would maybe try to get rid of), which is part of the regular Magic gameplay. Furthermore, your designs won't be as restricted. As with the Force and Temple I mentioned, you can make cards that play into the theme without being small creatures themselves.

That's actually a very sensible comment (if perhaps a little too wordy, to be honest XD), and had I gotten the chance to playtest the mechanic (which I didn't even really get to offer up at Goblin Artisans), I might have gotten there. It certainly carries over the correct flavor of "protecting the underdog". Once I'm done answering your comments, I'll probably change all the cards over to it.

Glad to help, and will try to count my words next time. :)