Harmless enough if you are just making images for fun. But probably not an ideal workflow for real work.
It can be, and usually is by default. If you set the seeds to deterministic numbers, and everything else remains the same, you'll get deterministic output. A slot machine implies you keep putting in the same thing and get random good/bad outcomes, that's not really true for Stable Diffusion.
You yourself acknowledge someone can better than another on getting good results from Stable Diffusion, how is that in any way similar to slot machine or rolling the dice? The point of those analogies is precisely that it doesn't matter what skill/knowledge you have, you'll get a random outcome. The same is very much not true for Stable Diffusion usage, something you seem to know yourself too.
Hmm. Ideal is rarely an option, so I have to assume you are being careful about phrasing.
Still, despite it being a black box, one can still tip the odds on one's favor, so the real question is what is considered 'real work'? I personally would define that as whatever they you are being paid to do. If that premise is accepted, then the tool is not the issue, despite its obvious handicaps.