About the expectations of investigative results

[callforjudgement]

I think it's most important that there's a known level of doubt.

A Cop result has very little doubt in a Normal at the moment, as most roles that can interfere with it are banned (and Miller is normally claimed).
A Gunsmith result has considerably more doubt, because there are a lot of known ways it can be interfered with and it's likely that one exists in the setup. (And even if it doesn't, scum can often claim out of a guilty.)
A Tracker result has rather one-sided doubt; if you track someone to a kill, they'd better have a pretty good explanation, whereas if you track them nowhere it doesn't really confirm anything until there's only one scum left.

All these roles are usable (although Cops typically need some sort of modifier to prevent the game being excessively swingy, unless the game is very small).

On the other hand, a role which has an unknown level of usability pretty much comes down to modWIFOM, which is normally considered undesirable. If I aim an unknown-quality investigative role at someone and it says that they're scum, what am I meant to do with that? And if we lynch them and they flip town, should the town then immediately lynch me? So although the ability to paint doubt can be valuable, people should know the circumstances under which it happens. (I've played many games offsite where it's known for a fact that there's a Mafia Tailor in the setup. I don't consider that problematic, even though I think a hidden Tailor is borderline bastard.)

[callforjudgement]

In role madness games, it pretty much has, because night results tend to give enough information that the dayplay is almost worthless.

In more role-light games, though, dayplay (including pushing lynches) is alive and well.

[callforjudgement]

That's nearly always an incredibly bad idea as town.

I also think it's not done nearly as often as it should be as scum.

[callforjudgement]

To me, one of the main determiners of whether something is bastard is whether it can act in a way that the players can't reasonably predict.

As such, the extent to which something is bastard depends on the metagame and common modding practice. ("Cop of unknown sanity" is IMO a role in its own right, and not bastard if expressed like that. So long as it isn't a random cop, because that's a terrible role.)