So I've been playing this game since the golden age where you had an ANY in ranked and other interesting NK possibilities for the game. Nowadays it feels like it's so dumbed down to every game "tp lo I'm jailor" "vfr 1-->15" that the game is ultra bland and boring, but that aside, I've been playing for years and there is something that always pissed me off.
Throughout my entire life playing competitive games, I've never seen such a TRASH and unbalanced role in a game such as Arsonist.
It is just IMPOSSIBLE to win, REGARDLESS of what you do or your skill level. This role was so bad, that I remember that back in the day where you could see who was doused in the night, this role had a ridiculous 99% lose ratio which is unheard of in any game that has a constant balancing and ranked modes. But the saddest thing is that even after YEARS and some major buffs, this role is still pretty much the same. The only way you could possibly win is through ABSOLUTE sheer luck.
In all my games I played as Arso I never managed to win once, doesn't matter what I did right or wrong, even in the best possible realistic scenario you'll be left 1 v 1 v 1 with Mafia vs NE vs Arso, and it's totally out of your control whether the NE helps you or not, so it doesn't even matter if you played perfectly up until this point.
To make my point clear, I mapped down some conditions that Arso requires in order to win the game by himself, using his own abilities and skill plus some other in game factors that are out of his control.
1 - Manage to douse and ignite all your targets.
2 - Kill all townies and some mafia so you do not get outnumbered.
3 - Try to misdirect the attention of yourself by playing as a townie.
4 - Do not get targetted by Jailor.
5 - Do not get roleblocked by Escort OR Consort.
6 - Do not get transported or that might screw up your targets.
7 - Do not get attacked by Mafia when there is a Spy in the game.
8 - Do not get invested when you try to fake another role to make condition 3 more plausible because bg gf arso is a very weak claim and insta lynched.
Now it gets fun
9 - The TARGETS that you doused should also NOT get targetted either by Mafia, NE Jester or Exec, TK, or Jailor. Why is that? Simply because you lose one night and one kill potential, making your role even more useless.
10 - Get in a scenario where there are Mafia vs Arso vs NE and NE must vote for you so you can win.
11 - Do not get targetted by NE making fake plays on yourself or Witch controlling you to someone else that could mess up your douses.
12 - Do not visit an alerted Veteran or get Witched into it.
There are probably more conditions to win but I think we can figure it out at this point that there is just too much out of his control.
Now let's take a look into the LOSING conditions
1 - Literally ANY of the 12+ happens with you.
That is right. If you don't have an absolutely perfect game, there is no way you can win, unless town or mafia throw and let you win because of memes.
In comparison with the other NKs, let's take a look at Werewolf and SK winning conditions:
Werewolf
1 - Do not get targetted by town or mafia early on. But you can still get roleblocked, transported, even invested. The only thing that could cause problems is getting attacked or interrogated by Sheriff on even nights.
2 - Kill more than 2 people in N2 and get away with it.
3 - Play as a townie and misdirect the attention from yourself.
4 - Manage to kill enough townies and mafias so you do not get outnumbered and be left in the same Mafia vs NE vs Werewolf scenario, or get help from townies in the same scenario.
5 - If Witch goes for you, manage to convince her to play for your side.
SK - Pretty much the same as Werewolf, but you can get more consistent results since you can kill all nights, but also you can get screwed by esc/consort. SK is still easier and more consistent to win compared to Werewolf, but those two roles also require great luck and skill and hard work to pull a victory through.
If you compare those 3 you will realize that different than the other NKs, Arso can't be targetted AND ALSO his victims, so It's totally ridiculous principally because he can't kill in all nights and requires 2 nights to get a single kill, and he can be blocked by pretty much everything. The fact that he has an Unstoppable attack makes little to no difference because he cannot kill enough people for him to win and there is too much out of his control.
My suggestion is simply to bring the Plaguebearer back because that role was awesome, or just buff Juggernaut and bring him back and completely remove Arso from the game. You can ask any player in the forum and I guarantee you that not a single one will claim that they have fun playing Arsonist unless they have some issues in their head or just like to troll all games.
Or you can simply buff Arsonist to make him playable by giving him more killing potential.
One of my ideas is the following:
1 - Keep pretty much everything he has but remove the "douse causes invest target to see as bg gf arso"
2 - Dousing your target makes anybody that visits the target to be also doused.
3 - Unstoppable attack reduced to Powerful, which means Doctor can save an ignited target.
This way you will also nerf the stupid meta of "tp lo" every single night giving pretty much immunity and the same strategy to town every game because people will be scared to visit if there is an arsonist on the loose. Even so, the LO can still easily out you so it's fair.
The problems with Arso will still not be solved, but at least by giving him more killing potential then he can be at an even ground with the other NKs.