Well, today I tried 3rd slot for the first time and found alchemer switching harder, since I always use "wheel down" for weapon switching. I often find myself swinging Grintovec in a place where I needed to shoot.
My suggestion is adding the option to lock weapon slots. A weapon in a locked slot can't be switched to, but can be used by its hotkey.
For example, I got Voltech Alchemer Mk II, Shadowtech Alchemer Mk II, and Grintovec.
By weapon switching at the same direction, I get something like that:
Voltech>Shadowtech>Grintovec>Voltech>Shadowtech>Grintovec>...
Grintovec hinders my alch-switching, but it is supposed to be a "support" weapon.
Now if I lock the 3rd slot,
Voltech>Shadowtech>Voltech>Shadowtech>... 3rd slot hotkey: 3
Now I can alch-switch properly, and just press 3 to switch to Grintovec where I need to.
Don't bring a Grintovec at all. You can just solve your problem by moving your wheel up and down, not down, down and down.