What if a two year old toon gets a rework a week after you zeta'd that certain toon at a discount. Since the radical rework, let's say you get an investment refund. Will the system keep track whether you invested the full price or a discounted amount of zeta materials in that toon? Does everyone get 20 mats back?
What if a 3-4 year old toon suddenly becomes part of the meta, due to a new toon added that synergises well with it? Do you expect CG to let you farm that toon at double speed and reduced gear requirements?
These are just some of the loopholes. Probably older toon shards could be more accessible, but not gear and zeta materials.