Making it inconvenient is something that then becomes annoying for a whole host of other reasons. Your side takes a beating and you lose an engineer, and suddenly it's a huge blow to you realtime-waiting-wise. Or you always need to keep an engineer with your ark so you can make more engineers. Etc.
I'm not trying to be difficult, but it's the sort of thing that players start doing immediately.
Having N sliders is clearly a problem, though. But then potentially that means we need a "Scotty screen," and we have a single screen that shows available scotties, planets that you have that are able to construct something, and you click them to assign up to N scotties to a given system. You can't stack more than 3 scotties per system, perhaps, as a neat twist. So if you have a pool of 20, you're actually best encouraged to spread out at least a little.
I'm just speaking off the top of my head here. But basically in the past we often made things extra difficult for players because we were reluctant to add new interfaces. I'd rather have a ton of interfaces that are small and simple and directly to the point (ala Cities: Skylines, as one example), rather than trying to go so interface-anemic that things become difficult for the player in other ways.
The fact that we can create interfaces much quicker and easier now is one thing that helps with that, but either way the data under the hood is the same.
