This is a sitewide issue and not within the scope of the Wingspan implementation specifically. I understand the frustration, especially for Wingspan since so much useful information is shown during final scoring. In addition to what you mentioned, conceding also excludes the table from any statistical analysis. From within this implementation there isn't anything I can do that wouldn't revive worse problems. BGA does not allow conceding when the game progression is reported to be less than 50%, which I infer was put in place to inhibit Elo farming or trolls ruining games by joining just to immediately concede. If I were to modify this implementation in a way that "hacks" its interaction with the main site by changing the game state progression to below 50 near the end of the game, players would
leave instead of conceding. When players
leave a game in progress, they lose Karma points and their Elo is affected in proportion to the game state progression (
see FAQ for more info). Before
leaving came with an Elo penalty, this led to very frustrating outcomes where players would not play their final turn and just wait to be kicked from the game (or gambling on another player leaving first and getting the penalty) in order to protect their Elo rating, since Karma can be recovered easily. I experienced this several times in real time games when I joined in 2020. At least with concession, the main site treats the game as a win in your favor.
An idea
suggested on the Wingspan forums would be a good idea in my opinion - there should be an upper bound for concession as well as a lower bound, so that for example you can only concede if the game progression is between 50% and 95%. However, as noted, this would have to be something handled by the main site, not the Wingspan module specifically.
There are a few open reports I found addressed to the main site, where the issue could be properly addressed by the main site team.
https://boardgamearena.com/bug?id=19843
https://boardgamearena.com/bug?id=85415
Edited to correct language: abandoning vs. leaving a game in progress.