A bit late to reply, and just adding a few comments on how the change happened from a perspective of a half-way player. I was a returning player, with stats so insignificant, which had then grown to a reasonable numbers through farming.
In short, the progress was painful at first, not to train, but to grow the necessary inventory slots and the prices of the more costly creatures.
I have but a single commentary on the process: You are not gated by the creature costs, other than early on. You are instead gated mostly by free slots, and the efforts required to train these crits.
The changes struck me as odd: the result being far, far from intended. There could have been more, much more methods that isn't so terrible as one you had chosen. Let me be blunt: The change had little effect to long term players, who could proceed to farm as much as they are willing to spend the time to. Further down this reply, I shall demonstrate this effect with simple graphs illustrating my points. In short: this update effectively make training extremely unrewarding, boring, and bad for those without the stats to start recruiting.
Let me start by commenting on the intended purpose of these change: To gate the process through which a player gain new statistic. The intention is clear, but there's no sense of direction of how you wish to approach it, nor any efforts to envision what results you wanted.
First, the rates through which an account may grow its statistic. What should have been the question, is to ask how fast people are acquiring them, at which stage of the game they were, and then deeming it acceptable or not. The rates for Vit, more likely than not, correlate directly to how frequent one is, whereas Vp, how frequently does one bother to purchase eggs. While the number of eggs one can keep and grow their Vp could grow beyond reasonable, the rates one may grow their Vit is almost dependent on their efforts in the realm. Both of these, however, are linear, unlike those provided by the shop, which is exponential. A linear growth is the very least, desirable, and does not propels out of control. From then on, there should be a question of how fast this rate should be.
Second, the cost growth of recruiting, compared between Aia's measure, and the solution implemented by Mur. I shall provide two graphs, one of the individual acquisition cost, one of the total acquisition cost:
Unit cost
Accumulative cost
The unit cost shows that Mur's formula is outscaled by Aia's during the 16 crit range, while the cumulative cost is taken over at around 21. This implies that Aia's formula is far superior to the desired goal, which baffles me as to why the alternative was chosen.
However, this does not interfere with the fact that the cumulative cost to recruit a number of creatures is still a static number, a number which does little to gate those with far superior status, but a lot to deter those new to the realm, nor simply possess inferior numbers. Had it been the case where not only one's stats, but also their free slot, and their utilization of these free spots, to increase, which implies an exponential growth, the solution would be much deserved, but alas, it isn't. One may aim to grow 15-20 at a time, which then is simply the question of if they are able to reach the now elevated cost to acquire such creature in a single batch. What would happen, however, is the march toward such goal would become much, much slower. On top of which, if one choose to own a few of said creature for usage, would bump the starting cost even further, and the resulting final cost much, much further as well.
I must suggest that a proper goal to be set, and a carefully engineered solution be present. Directly related to the issue, perhaps it's the reward of each individual creature that should be tweaked to yield the desired outcome.