My feeling is that you are comparing very different things:

• Small image: not sure how small it would become if we made it do what Tails must do.
• Fast boot time: not sure how fast it would become if we made it do what Tails must do.

It maybe be worth reading our specification.

Puppy builder: how is it better than Debian Live toolkit in a way that would save us time?

So until now, I've seen no compelling reasons to undergo the major effort needed to switch to Puppy.