The argument goes like this. Games seem to have 2 primary (which are obvious, at least to me) purposes.
Entertainment
The practice of certain virtues, the most pertinent amongst most strategic board games (in my view) being perspicacity, concentration and patience.
I argue that Go manages to, if not teach virtues such as these, at least remind someone of them. The difference between teaching and reminding, in my understanding of the terms, is one of degree, not of kind. I don't know whether any game can teach virtues, by which I mean, I don't know if a game can cause someone to change their habits by reminding them of the importance of certain states of mind with sufficient frequency so as to make a notable change in their lives, but perhaps a game can cause a person to enter these states of mind, and remind someone of the importance of those states of mind more frequently than if they never played the game, regardless of the size of the change on the persons life (I realise that I have left the definition of what is considered a "notable change in their lives" up in the air here, which I have set as the primary distinction between a game being able to teach and being able to remind a virtue, as I am uncertain as to the extent to which Go can influence the psyche of different persons).Now why can Chess not concentrate the mind towards those virtuous mental states described above? I argue that due to the characteristics of Go, it is difficult to play the game without concentration, or patience, or without exercising perspicacity. What's more, it is difficult to learn the game without exercising these qualities. It is easy enough to learn the basics of Chess, to play many a game against persons of similarly significant ignorance, and yet to get a basic feel of what is going on and an excitement from realising when victory is near, which is often evident even to beginners. Go, I believe, is, at least initially, an unpleasant game for beginners on account of the purported greater initial difficulty involved in learning the rules and and learning how to play decently (A statement based on my experiences of arguments on r/baduk and https://lifein19x19.com comparing Go to Chess in this regard). Some familiarity with the game is needed to understand this point. All the reader needs to know is that the goal of the game is to capture territory, by placing stones on the intersection of a 19-by-19 sized board, though beginners often practice on smaller boards. For those who want to learn more, the basic rules can be learnt here https://online-go.com/learn-to-play-go, whilst puzzles and introductory strategy is taught here https://online-go.com/puzzles.
Compared to Chess, whereby the main principles of the opening consist of development of pieces and control of the centre, objectives which can be clearly perceived on the smaller chessboard, the game of Go spoils the player for choice, requiring the beginner to engage in some kind of study if they are to learn at a reasonable pace (it is obviously not impossible to learn through trial and error, but I believe it is far more tedious to do so in Go as compared to Chess due to the larger number of game states). As a result, they may be less likely to deviate from established theory in their initial development as a player, facilitating their development by basing it on a solid foundation, whilst it is easier to develop bad habits in Chess whilst playing against similarly unskilled and ignorant players. But if two Go beginners without any knowledge of theory play each other, the game is not fun for either player, as the range of choice coupled with their ignorance means that they lack even the joy of achieving an accidental victory as might be the case in a blitz Chess game, for blunders are much less evident in Go, a victory which can only be achieved if the Go players choose to play a game lasting generally longer than a Chess game in which the amount of confusion per move likely exceeds that of a beginner’s Chess game, and which only ends when both players “pass”, which requires a recognition on the part of both players that the game has ended because there is nothing more to do (Such that even the process of ending a game of Go requires knowledge about the the game!).
Unless one has a certain degree of patience, and potentially some other qualities too, which might be in greater abundance amongst regular Go players than amongst people who play chess in a half-hearted but regular way, then improvement in Go is impossible whilst also being demoralising due to the sheer ignorance that causes the losses, whilst a half-hearted chess player can play thousands of games without really improving, whilst still deriving a "kick" from the odd tactical snipe, an experience which proffers a reward but which does not force the player to practice the virtues necessary to play better. I say this having been one of those chess players just described. The only evidence in favour of this statement which I am employing is my greater ease of frustration in playing and learning Go as compared to playing and learning Chess.This situation seems even to apply in the case of intermediate players of Chess such as I, such that the primary joy derived by me as a Go player seems to be the acquisition of knowledge of my ignorance, whilst in the case of Chess it is difficult to remove the lust to win as the primary goal because the victory is indeed closer in sight in Chess game than in Go, and so the process of realising that the game is but a vehicle towards the achievement of virtuous mental states may occur more slowly by playing Chess, I suspect.
And to give a minor argument in the vein of Chesterton's Fence (minor, because what I will describe does not apply to all Buddhist sects) for the ethical value of Go, which is dependent on the extent of your agreement with Buddhist ethics, there is evidence that Go was considered useful in the regard which I described above, as Buddhist monks of some Japanese sects, notably the Nichiren sect, played Go as a means of practicing the virtues conducive to enlightenment (this article explains the relations between Buddhist ethics and Go https://tricycle.org/magazine/the-game-go/#:~:text=This%20is%20the%20game%20Westerners,life%20as%20Buddhists%20understand%20it). One of the greatest early Go masters, Nikkai, was a monk from this sect. I am not familiar of any Christian sect having used the game of Chess explicitly as a means of honing their moral sense.