I can’t help but disagree with the most Part of your Arguments.
First of all “Easy Layout” is absolutely Arguable, and most People yourself included argue at this point with a certain bias. If you are used to a layout for 15-20 Years, than no matter how good the new Layout / Forum-Type is or how bad compared to old one, simply for the fact you are used to the old one, you will have a easier time. If you take a step back and look for “real” newcomers which never was in touch with GD’s old forum, and / or overall don’t have much experience with the classic-style layout / forumtype, AND if you take your time as a “old user” to get into the new type of Forum, you will definitely see the qualities of discourse, and i’d go as far for Newcomers it’s more accessable and easier to get into.
You can believe me that i struggled with the new Forum as someone who used the classic Forums like 14 Years, even so far that i really disliked it at first and never got into Gearbox Forums anymore once the shifted towards Discourse. However this past Months of getting used it, it kinda grew to me and now it’s on par with the traditional Forums, if not even in some regards better than the old one. Borderlands / Gearbox however was a different case, because i wasn’t as geniunly invested as in Grim Dawn to really bother, which leads to my next Point.
Most Newcomers and Average People won’t use Traditional Forums anymore anyway. I’d say the first place where such individuals visit and most likely stick to it, simply due it’s fully implemented feature for a tool which you need to play the game anyway, is the Steam Forum (except GoG Users obviously). I’d argue most People who go as far and go to an official, browserbased Forum have overall enough interest and will to get used to a new template / layout / forumtype. So from my Perspective, the type of players you argue won’t bother with the new forum, wouldn’t bother much for the Forum overall due they would visit these forums rarely / casually and as such, aren’t really the target audience. Combine it with the Fact that the Devs like the new Forum better, and regular users seems to like it (or don’t mind) the new Forum, i’d say it’s not a big loss if such people as yours mentioned would “not bother”.