I use a MBPro 13" and an iPad.
There is obviously overlap of capabilities, but they do different things. If I'm just chilling on the couch, eating some snacks, and watching some Netflix, I'm not using my MBPro. Sure, I could, but if I'm risking spilling stuff on my iPad or MBPro, it's obvious which one is the higher risk item. But then if I'm surfing MacRumors on my iPad and need write a semi-lengthy reply, that's not happening on my iPad. So I might open up the MBPro for a short while and use then, then switch back.
But as you said, you need macOS software, so you're limited there. Maybe it's an iMac and MacBook (non-pro) combo you need instead? That would cover you for macOS, and give you options for portability and horsepower.
There are obviously answers that are "wrong" but in terms of "right" answers you won't find that definitively from a couple of half-arsed paragraphs 🙂 So yes, it might be pointless to have both. Or no, it might not be. It depends on your preferences and uses.
As a general rule though, I don't do any "real" work on my iPad. It's for surfing, reading, GarageBand etc. I know some people do some photo editing and real office tasks on iPad, but for me I'd much rather use a real laptop of desktop for that. Again, there is some significant overlap between the capabilities of the devices these days for sure.