I think the real issue with Brock isn't his skill or talent, which are of course very high, but the corner WWE has booked themselves into with him since 2014 where he's a special attraction with classic special attraction booking, but it also makes no sense for his character to be involved in anything except the title scene, and also he's nigh unbeatable. It'd be like booking Andre to be the champion for most of the 80s so not only is your champion rarely around so the title scene is held hostage, but also anyone who gets over enough to face him is going to get smashed and still have to be on TV every week while Andre doesn't come back for 3 months.
Because of this, everything he's involved with is the same and his feuds have benefitted no one, not even Seth/Roman actually beating him (twice in the same year in Seth's case). In fact in almost all cases it has derailed his opponent's momentum (Reigns, Rollins, Strowman, Joe, Ambrose, Balor, Orton, Kofi, Rey, Ricochet (lol how did that even happen)) to the point it took them years to recover or not at all. It doesn't even seem like he's done anything for ratings or ticket sales, either.