I don’t think there is anything inherently better about mecanum wheels either, but there are some advantages and disadvantages to them which make them a very viable and competitive option in the right hands.
There are many reasons why mecanum (and to a greater extent, all non-tank drives) do not typically win worlds. Like you mentioned, many seasons are less suited to holonomic drives. Holonomic drives also require a lot of investment before they benefit a team. You have to put in a lot of additional programming and driver work to make them competitive, and the vast majority of teams make the decision to instead focus efforts on refining a simple robot. Simplicity is almost always when ends up winning in the end, just because by the very nature of vrc, having a super consistent, simple bot with a ton of driver skill will usually win in the end. As to why mecanum drives are generally disliked, I figure there is a number of reasons as well. Many teams are unable or unwilling to put the necessary effort and skill into properly using holonomic drives (which is totally a competitive and viable decision to make, I would never recommend holonomic drive to a team that prefers tank.) Also I see a lot of people bashing mecanum wheels in particular, which causes teams who have never even tried them to just assume they must be bad.
of course they have their tradeoffs, they are bulky, heavy, worse at pushing and defense, and I’ve heard they suffer under inconsistent and unwieldy center of mass. X drives as well have other disadvantages, they are arguably bulkier than mecanum, and much more complicated and difficult to build than mecanum.
But to everyone who thinks mecanum wheels are inherently bad or non-competitive, I suggest you give this a watch and reconsider your perspective.
In the right hands, mecanum wheels can be a very competitive and perfectly viable option, and I do think this game might have the most potential as a mecanum-friendly season yet. There is no robot expansion, so center of mass will remain constant and central to the bot. There are not really any climbing obstacles (other than potentially the low goal barrier, which is pretty small and could easily be driven around, as I imagine intakes on most bots might get in the way of traversing that). And strafing seems particularly useful in this game, for efficiently collecting and aiming shots.
I have experimented with mecanum wheels before, but never used them in competition, as I, like the large majority of teams, was perfectly comfortable with tank drive, and I knew that my programming ability was not good enough to make good use of them, and though I knew I could certainly improve my programming ability to make mecanums competitive for me, I chose to instead use my time to improve other aspects of my robots. But I think if I was still competing this season, I would be seriously considering mecanum wheels. Possibly with a 6 motor 6 wheel setup, similar to interesting asterisk drive setup mentioned here.