A coincidence that indeed gets pointed out from time to time!
I only played Star Ruler 2 after I made the original PICO-8 version of Slipways (prompted by a comment much like your own), and I must admit, the ideas around resource delivery and the resulting "leveling" of planets are very similar. They're very different games in all other regards, though.
In my case, the inspiration for how the resource/leveling system works was the original Railroad/Transport Tycoon games from the 90s :)