So I'd like to address this part. While I'm also anti-ban, I do appreciate the arguments of the people who are asking for Diglett to go, mostly that Diglett has a huge effect on teambuilding. There are many Pokemon that are just flat out unusable on certain team types (mostly balance cores) due to how Diglett can disarm them incredibly effectively. Say you wanted to make a Ferroseed and Skrelp core for your team. Unfortunately that Mienfoo you switched to Skrelp from Ferroseed on just used U-turn and now half of your core is dead at basically no cost to your opponent. And even then Diglett doesn't give away momentum since it honestly is fairly powerful and has a good movepool. What this does is push the metagame towards offense, which some people do dislike and feel that the (more stally from what I've seen) Digless metagame which has 'more' diversity is better.Sure, Diglett is annoying. But it isn't dominating anything, or shaping the meta around it any more than other top tier threats. Diglett isn't even unique in what it does, if one really wanted to, Trapinch could be used to secure a KO on many of the same things Diglett can (Including Diglett, humorously enough). Diglett does not require particular attention when teambuilding, since checks to Diglett are rather common. While it does mean that some pokemon are basically unusable while it is alive, this is no different than the effect that Dugtrio has, and Dugtrio chills at RU despite this trick. Really, that's all Diglett has going for it. A trick. If properly prepared for, it is really no more of an issue than, say, a Sturdy+Berry Juice trick, or a standard weather team. It has a trick to disarm before you can get at the squishy center.
The numerous checks to Diglett is a kind of irrelevant point. Sure, it's really easy to check, but the thing is that Diglett usually gets to choose when it comes in. I hope you weren't expecting your non-flame charge Ponyta to actually get any kills during the match. The way that Diglett requires attention in teambuilding is virtually the opposite of almost any other kind of threat - instead of saying "oh shit fletchling runs over me I need to add a counter" it's more "oh shit Diglett literally kills two members of my team and I can barely do anything about it, better replace at least one of those", it restricts your teambuilding not by forcing you to run something in one of your six slots but instead causing you to not run something in a slot.
The effectiveness of Dugtrio shouldn't really be considered. Dugtrio has, relative to its metagame, much lower attack than Diglett and even less speed, which is compounded by the higher bulk of level 100s (yes even without Eviolite). Diglett is able to trap and kill many more targets in LC than Dugtrio can in RU or OU. Besides, fully evolved forms shouldn't really be a factor for their base stages: see Gothita who has exactly the same "trick" as Gothitelle did. And on that note, trivializing it as a trick is kind of understating it. It's a "trick" maybe, but it's a damn effective one. Previous banned Pokemon also had a 'trick' like Yanma's Compoundeyes Hypnosis or Swirlix's boosting sets. Sure, Diglett won't exactly be sweeping full teams, but it's a support Pokemon, which is kind of a hard concept to grasp in comparison to previous suspects.
Diglett is effective. FletchDig, DigFloon and ShellDig teams have been proven quite successful. I'm anti-ban because I don't think that these cores are overwhelmingly effective to the point of very limited counterplay, and I don't think that banning for diversity's sake is necessary here since Diglett isn't wrapping the metagame around itself and causing a much more limited number of Pokemon to be viable. With the sheer amount of innovation that has been displayed by LC players in the post-Misdreavus metagame I'm not sure you can really say that this metagame is limited with Diglett in it. From what I've seen on the ladder, there's honestly not that much more diversity, in fact I haven't seen anything even slightly new other than bad sets like Scarf Machop and SubSeed Leftovers Cottonee. This contrasts to my experience in the last test, where sure I saw a whole bunch of Diglett and Gothita but I also saw some really cool stuff like Bulk Up Rufflet. What the ladder has shown me has been actually against what I halfway expected, to my partial relief, the metagame without Diglett is not overflowing with way too many threats. In fact what it's shown me is a lack of diversity; Diglett leaves and about five Pokemon become significantly more viable which results in many less established things being left by the wayside. Yes this is a ladder for reqs, so it's not the most accurate picture of what it could become, but that has been my experience with the ladder.