In the past I've used a few online writing pads that had a chat function included so you can communicate while you write. Later there was Google Docs that held the same features with additional benefits of being a better mobile platform. Discord is just another stage of this with its ability to talk and discuss live, to link information and pics, and have a few fun and personal customisations.

What Discord does is allow users to easily communicate with each other — Key word in that sentence: Easily. Because of this the OOC page of the threads do become less populated with people opting for an easier option to let their peers know that they are posting and what they wish to reply with. You can check with your GM about a variety of aspects and, if lucky, almost obtain an answer instantly. At the same time I do feel that it has become a distraction for IC writing with talking to your friends being made so accessable, however [@Nytem4re] and [@Saint Maxx] are both correct as well in that a flaky writer will always be a flaky writer no matter what platform of communication is available.

My believe, if we do wish to venture into the topic of committed writers for a moment, is that GMs today are placing way too much effort into an OOC to start off with and they're not getting the same return in players, commitment, or posts. Rather than letting the players imagine and build up the words, they write out aspect of the world or answer questions by the players in a way that narrows the RPs possible scope. People in turn become bored because they've somehow cheated their way to understanding what the RP and story is all about and end up leaving. Discord does impact on an RP in this manner as spending an hour chatting about an RP can be a lot different to a handful of posts where you have to wait for your GM to reply to answer your queries.

As for clique warfare, it has always been around; it's just easier to link up with others who have the same view and opinion. Venture into Reddit and you'll see toxic people, venture into Twitter and you'll see toxic people, and even on Facebook where your friends have a real life name and description of their life and you will see toxic people. The issue with RPG is that too many people place this toxicity and clique warfare above their roleplaying experience to either spend the time arguing with each other and not RPing at all. This is a limited interest site with only a small selection pool of people, and all you will be doing is harming the growth and potential for players to join your RPs if you involve cliques.

To end on a reply for a quoted section: 
[quote=@Lord Wraith]I have had mods delete posts in the OOC of my threads to avoid drama spreading only for players who were offline at the time to direct message me to find out what was deleted. This has also extended to players messaging me privately to bash on a sheet or player they don't like and unfortunately I too have displayed these same behaviours from time to time. 
[/quote]

This is where all your problems lie. A GM should be doing what they can to stop the bashing of other player's work, and in turn they should not be so negative. If you want to stop clique warfare then you have to do what you can in not being a part of the problem. You wanna bash, you wanna bitch, you wanna exclude someone from an RP as a GM? Then you have to expect your RP to potentially die. No amount of threads or discussions will help if you want to display to your players that bitching about someone is ok while you're the GM. If you don't want someone to join, just tell them this RP is not for them — what they do after that is up to that individual, but don't flame the fire when it is not needed.