How important key is balance in the initial play-test of a game? Should be relatively unrestricted and only loosely balanced? Should the first few play tests done to check if the general game mechanics themselves are fluid rather than the Units themselves, which would later be refined to a more balanced state?
Specific numbers should be refined later. Initial game design should focus on fundamental balance of mechanics. For example, a specific strength of a character card or it's cost can be tweaked as needed, but a mechanic like "when a character deals damage, draw that many cards" may be fundamentally unable to be balanced.