I don't agree with your team's assessment. I disagree with your definitions of tools (I mean, extending your logic, an inclined plane is a tool so then that is illegal too, and furthermore the battery charger or drill used to repair your practice bot is not used on anything -- directly at least -- relevant to the game or real robot, since construction of a non-competing robot is analogous to construction of giveaways in the grace period), and I disagree with your interpretation of the rule's spirit; as Joe Johnson
pointed out, this is more of a mercy rule than anything, and in that regard I do like FIRST's putting it in this year.
I think the biggest evidence this has nothing to do with practice robots is that if FIRST didn't want teams shelling out money on practice bots to give themselves an advantage they would have just said it.