Capital Games TeamThe problem isn't that R9 is a "bad" investment, but rather that the stat bonuses are worth the cost of such expensive/difficult-to-acquire items. As is, R1-7 seems to be in a great place in terms of scarcity. It takes some farming, but it isn't a huge deal to take a character to R7, and the stat bonuses you receive at those various levels seem to correspond well with their cost. R8 and R9 are a big investment, and those stat changes do NOT seem equivalent to the cost.
If you want to introduce this relic system at a wide range of relic tiers (rather than just for R7-R9), there likely needs to be an exponential multiplier applied to the materials required for each level. R1 materials can stay the same, but R2 materials should be made a tiny bit easier to acquire than they currently are, and R3 should be made easier to acquire at a slightly higher rate than R2 materials, etc.
If this change to relic materials is made upfront, it would be a 1-time change that then would likely not need to be adjusted in the future (or very rarely), and would make scalability much easier for the future. I also believe doing it in this manner would drive away the fewest players, long term (though not a perfect solution, as it results in the game being significantly more difficult and unsatisfying in PvP for underdog players, which is a big motivator for developing and refining strategy in SWGoH).