When Jobs introduced the iPad in 2010, he clearly did not see the iPad as a laptop replacement. He called it a third type of device that sat between the smartphone and the laptop. He said for there to be a third type of device it must be better at certain things or it has no reason to exist. In particular, Jobs referred to mail, web browsing, photos, ebooks, instant on, long battery life, thin/light, and a few other attributes that would justify this third device. He also made the case that netbooks (which were popular) were a poor solution because, in his view, they weren't good at anything....just cheap. Basically, Jobs made the case that a tablet was the answer to this third type of device.
Then, later in 2010, Apple released the redesigned MacBook Air at a much more affordable price. It had solid state drive for instant on, relatively long battery life, and it was light and portable. As Job's said, the MBA was Apple's version of what would happen if an iPad and MacBook hooked up. This narrowed the gap between laptop and tablet. As MacOS and iPadOS have evolved, the gap has closed further. MBA battery life now exceeds an iPad. A fully accessorized 12.9 iPad Pro is more expensive and heavier than a base MBA. Gap gets smaller still, and some of the advantages of the iPad start to disappear.....but, some of the advantages of the MBA also diminish because the iPad has become more capable.
Hence the debate. For me, if I am only going to have two devices, it's a no brainer: MBA + iPhone. But, I can understand how others might see it differently. My biggest reason is that the MBA is just better at two important functions: Productivity Apps (iWork/Office) and Multi-tasking. I am retired, but I still do some work on the family real estate business, and these two functions are important to me. On the other hand, I can understand how this might not be the case for everyone. So, choice is great.