Well they did put it in space, so that already necessitates some changes from previous games.
Systems aren't static blocks like provinces in EU, they are closer to mini-maps of their own in which units can freely move in 2 dimensions. I wouldn't be surprised if there was a performance or hardware reason not to make it a analogue zoom in.
In any case, if you literally can't spare a fraction of a second to hit one button, you need to play on a slower speed.
1. First of all, the function that that button serves is a clear indication that it could be changed relatively easily, just make the trigger for that function a specific zoom level instead of a button press.
2. Secondly, it's not that it's time consume to do once, it's that it's going to get real fucking old real fucking fast, as a coder i know that the number one most frequent complaint i get about UI, is things like tooltips, it isn't that it's time consuming to hover over a UI element, but that people despise having to hover over it
every single time they want to see that information.