You would have to prove that a company would fire employees lets say at age 59 so they can’t collect their pensions at age 60, if you can round up a dozen or so employees where this had happened, you can demonstrate that.
But an isolated incident where sales in a funeral home were down for three consecutive months without course of action from the employee who was well aware of the decline in sales. well that is going to be hard to prove that the funeral home owner hated homos unless the owner had a history of firing homos.
No, that is not how it works. Those would be an entirely different type of discrimination case, not disparate impact cases.
In a disparate impact case, the plaintiff doesn’t need to demonstrate that you intended any discrimination at all. The courts would just look at the results of your policies and then decide that, based on those results alone, you were either engaging in discrimination or not, regardless of your intentions, and regardless of any excuses you present.
So to adapt one of your examples, they could just say “Homosexuals make up about 3% of the local population in Smallsville, but they only represent 1% of the employees of your business located in Smallsville. Therefore your employment practices are determined to be discriminatory.”