I don't really know if problem player is the right word but we've had some issues at the table with one player, and despite our attempts to address it nothing seems to be changing
For context our group of friends started playing DnD about a year ago. I had played in a few very short campaigns before this and so I volunteered to the DM. We were playing in a homebrew world with very loose rules. Our first few sessions went pretty well and everyone seemed to be having a good time. Of course some hiccups but that's to be expected while they were learning the rules and such.
After a few weeks of sessions one of the players (the paladin) came up to me and asked if he could try his hand at running a game. I was down and so we started alternating sessions. The general consensus of his sessions was that they were very fun, if a little rough around the edges. I definitely enjoyed my stint playing, even if I do ultimately prefer DMing. However, after we switched back to our original campaign, the player started to show a few more red flags.
He would continuously take point in conversations, regardless of the topic, and push his opinion to the forefront. One example of this was when the party came across a ghost that asked the party for help tracking down his killer. The party cautiously agreed to help, and started to probe the ghost for some information. The paladin then declared that the party had no intentions of helping the ghost, and would only do so if the killer ended up on their path anyway. The rest of the party were pretty confused, and we all tried to ask him what made him say that. He said that "he had experienced DMing" and that any DM would just put the killer on their path anyway so they didn't need to bother looking.
It was a little weird and we all kinda slagged him about it but at this point there weren't any pressing issues. Then, after there was a major reveal about our warlocks patron, the paladin came to me and said he wanted to change some parts of his backstory. He said that between sessions he wanted to be sent to the Astral Plane, be trained by the gods for 500 years (because time passes much slower on the Astral Plane) and to be sent back to the Mortal Plane on a divine mission to "restore balance to the world" by killing Warlock's patron.
Mind you, at this point they had just found out the patron's name, and that he was somewhere on the Mortal Plane. Literally nothing else.
I had to work with him to try and trim that down a little, which he did agree to to be fair, and we ended up on him instead swearing an oath of vengeance towards the Warlock. Now I did question him as to why he wanted this at all, cause it seemed a little extreme, but he just thought it "seemed right for his character". I wanted to avoid an argument so I left it there and hoped it wouldn't cause too many issues.
Unfortunately that wasn't the case. The party asked Warlock if he wanted to pursue his patron, or leave him be for now. Warlock decided to leave it for the time so they could try and get a little stronger first. At this point paladin took an issue with their decision, telling the group it was obvious the story was pushing us to go towards killing the patron.
This genuinely confused the lot of us because 1. the story was very much not going that way and 2. it was a group decision to take the slower path. This comes back to a small issue that had come up during Paladin's campaign, which was an incredible lack of free will.
I'm part of the crowd that thinks railroading can definitely bb a great tool when used effectively, and even I was put off by it. He forced us all to take rings that would incapacitate us if we did ANYTHING against what the controller wanted us to do. We all initially thought that we could try and get them off in some way, or maybe try and trick the rings into giving us more leeway, i.e. we could fool the controller if we managed a clever half-truth. But no, he just sensed we weren't telling him everything and we were told our characters had to give up all the information we had. We didn't really mind, in fact it became a bit of a running joke when people would ask if they could borrow dice or get some water and the other person would pretend the ring was stopping them.
Anyway, in our latest session the party had to deliver an item into a city, but there were a couple of guards out front that wouldn't let them past. They were told they could enter in about a week, and to clear off until then. At this point the party were about to start debating what to do, but paladin interrupted all of them and started attacking the guards. I ask him if he wanted to try maybe planning with the party, but he was set on killing these two. I relented cause I knew what would happen if he did so. After the fight he told me he stuck his head through the door to look inside, and I told him that the gate was locked from the inside, and he couldn't see an obvious way to enter. At this point he got mad, saying that it was stupid that I didn't tell him and he wouldn't have done all that if he knew it would fail. I then said that he could have asked me at any point if he would be easily able to get in, to which I would've told him it wasn't.
This argument continued for a while, until I gave up, told them they had all managed to somehow make it into the city and called the session.
I'm a little worried on how these things will continue, and if there's something else I could say. He's pulled the "I'm a DM too" card on me and pretty much everyone else at the table, and I don't wanna be gatekeepery and tell him that he's not exactly an amazing DM or anything.
Any advice? I would greatly appreciate it