It's been a few years since I've played OU, and have been getting back into it recently, but I've also been reading over this forum, and have a couple of points to make.
First, it seems that Dugtrio acts as an amazing revenge killer, since most of the time if it's switched in, it's free revenge. However, whatever dies will often be a counter to Dugtrio, either using priority, scarf, or is simply in a higher speed tier, which is much more common since Home came to the meta. I know this isn't the main reason people want it banned, but due to its fragility, and the fragile nature of all three 'mons with Arena Trap, it's almost impossible to switch in to non-electric or rock moves without a Sash, or Eviolite and resisting the attack, thus making it feel like the best use is as a guaranteed revenge killer. There are plenty of things that fulfill this role, even if they're not guaranteed, such as anything with decent attacking stats with priority, or again, a higher speed tier. In other words, for this point, it feels like Dugtrio is just better at what it wants to do, and to me doesn't feel like warranting a ban, since it feels like it auto-loses to any form of priority.
Second, is what was mentioned above. Arena Trap, and specifically on Dugtrio, seems to only counter a very small amount of the most-used 'mons in the OU meta, yet people have been saying that because it can win 100% of the time against one specific 'mon, it deserves the ban. For as long as Pokemon has existed, there have been multiple Pokemon who lose against something else, they simply cannot beat it no matter how hard they try. It's how niches develop, it's how the metagame develops. My point here is, Dugtrio is good against some of those 'mons, but there's plenty more that beat it, in return, as well as being fairly neutral against the rest, or not working as people want it to. The point for this is, Arena Trap Dugtrio deserves to be banned, because it's a check to a top 'mon? And even not a hard answer, as it can't even switch in safely to Excadrill (the aforementioned 'mon), to either Earthquake or Iron Head.
I don't believe Arena Trap is banworthy, as it feels to be, at best, a tool for revenge killing, or in some situations a tool for killing an annoying mon or something that would otherwise be a check or counter to another 'mon on the Dug's team. But, that's really just like setting up for a sweep, similar to Baton Pass or something else similar. It takes skill to properly use Arena Trap, and it takes skill to prepare for it.
Thank you for reading, these are my thoughts, I hope they help in the decision-making process.