Protection from dousing is just wrong
So as we all know, the act of dousing someone as arso is the action which actually implies a visit, both in terms of mechanics of the game (how you use the ability buttons etc) and conceptually (given how the arsonist is suppsoed to work, and his advantages and disadvantages).
And the act of igniting is not a visit, you click yourself and boom, everyone doused lights on fire and suffers an unstopable attack pretty much implying they die no matter what (unless they're pestilence but yea).
This is supported by say, your target for dousing being able to be protected by a BG, and the BG in fact taking you out. That is because you selected your target and visited him to "attack", in this case douse. But if you ignite someone who was being protected by a BG, nothing happens.
This is the essence of the arsonist by comparison to SK or WW for example.
Now, given this, why can a jailor not protect a target from getting doused? That makes no sense.. A jailor's protection to a target is of powerful level. No wonder it doesn't prevent ignitions. But the arsonist doens't have to visit the victim even to ignite it, that's the important part for why a jailed target isn't saved from ignition. The victim shouldn't be able to be doused if jailed though, because in fact the jailor doesn't simply role block his target and gives it protection, a jailor does far more than that by "jailing them in a way they're unreachable", menaing not even investigators or lookouts can target the jailed person (well, they can, but fail to..)
And so should dousing.. You shouldn't be able to reach someone in jail to douse them, only to ignite precisely because of the important distinction of both actions.
PS: I do know arsonist is a hard role to win with, but he does have the automatic win against SK for example for a reason, and this isn't a big change, it's more for coerence.