I guess, it can be considered as borderline gambling as these gacha games or mini game from various games. Since the reward isn't monetary but some of it has value outside the game which can be traded from one player to another. However, most games doesn't allow transaction outside the platform to avoid this but still there are some games that allow them to be sold such as games from steam.
It depends on the person who owns it and what type of value that a person think about it where the value of the account could be monetary value, functional value, social value and psychological value.
I don't consider it as gambling since there is no way to win money from it unless I plan to sell my account for profit. Or if that game is able to withdraw some money then it can consider gambling but if not it will just be a game with buy in options like how some applications have when you want to access some features of that app. Though many is interested in such games that builds the character and some might sell their account once it is high rank.
I understand why you don't consider it as gambling because you can't win money unless you sell the account which I think reason of that or I may be wrong about it. I have seen it myself where a person created multiple accounts where he spend money to those accounts for a chance to win cool items or skins and then he sell it more than the money he spend which is profitable for him or some even found some bugs to exploit just to be able to get the desired items which the cost of getting the item is low compared to not exploiting bugs or issues (That's years ago to be exact and that's a different story). Anyway, gambling is not all about risking your money to earn money. To be exact, gambling has different types as I call it. The quote below will explain why I consider this as gambling.
1.) play games of chance for money; bet.
e.g "she was fond of gambling on cards and horses"
2.) take risky action in the hope of a desired result.
e.g "the British could only gamble that something would turn up"
As you can see, the second is about "take risky action in the hope of a
desired result" and when it comes to gacha game and other similar games where you can spend money to buy in-game currency that can only be acquired by paying real money which the in-game currency will be use to buy items hoping (taking the risk) you will get the item you desired.
That matter aside, I really do understand why you don't consider it as gambling as you have your own reasons why but to make things clear as much possible, the reason why I consider it as gambling is explained above. You have your own reason and I have my own. As you can see some people also considered it as gambling and some people are also the same as you. What I noticed many times is that most people will think right away that it is a chance of earning money by risking your own money when they hear/read the word gambling.