The advice of ‘just don’t get checked’ isn’t really a counter-argument to how good or bad a class is. You can say that about literally every evil and most neutral classes. Everyone is trying not to be suspicious (Except the fool), it’s a social deduction game. Saying don’t be suspicious is like saying “Win a football game by having more points at the end.” You’re not wrong, but it’s also not really useful advice.
Other classes have tools to assist them not getting caught, which the Alchemist doesn’t. Most of those classes have a team so even if they die they can still win, which the Alchemist doesn’t. Scorned and Fool have goals that means they don’t have to survive the entire game, the Alchemist doesn’t. If BD is hostile to Alchemists then being an Alchemist is almost like being an NK but without the benefits.
Which means that surviving as an Alchemist if BD is hostile to you is much, much, harder than surviving when they are not. Not impossible, and good play can certainly nudge your odds up, but the single greatest factor in if you’ll win as an Alchemist is the attitude other players have toward Alchemists before the game even starts. I’ve seen people win as Alchemist, but 9 times out of 10 people knew they were an Alchemist before the end of the game and let them live. And in the small time this wasn’t the case, it was mostly that the game ended very quickly. I’ve never seen an Alch survive a 10+ day game without being outed.
I know players who say you should keep Alchemists around and I know players who say you should always kill them. Those players have made their minds up in advance and there is very little an Alchemist can do to change their mind. All they can do is hope they get lucky and end up with the people who keep Alchemists around. No class should have it’s biggest (Not only, but biggest) factor in their winning or not winning be the strategy of the other players.