It's actually not quite so simple. The key thing here is lack of OcuSync. It makes a MASSIVE difference (versus the Spark, in my experience). I think the Mavic Air is a great drone. But it's not quite the Mavic Pro. It's definitely a niggling desire to want one, but yes - you can bet there will be a newer, fancier drone before too long to replace the Mavic Pro.
That's just the way it is. It's very much like Apple. They have different devices that have pros and cons (especially in the laptop world). I mean, for the most part I don't NEED a powerhouse MacBook Pro. I could do just as well on a 12" MacBook which is so light and portable. But the MacBook Pro has the cool TouchBar! And it has lots of USB Type-C ports! But the 12" MacBook has so much portability and great battery life! So then you want both. Poop!
The Mavic Air isn't better or worse than the Mavic Pro. It's certainly different, and there are things that will appeal to people about both.
Fundamentally, the Mavic Pro absolutely - UNQUESTIONABLY - will have better range and solidity of video transfer due to OcuSync. If you live in a city and do some fly-arounds, this will likely be the defining factor. It's not even about 4.3 miles vs 2.5 miles. It's about Wi-Fi flat out is not as good as OcuSync. Wi-Fi can be frustrating even 50 feet away.
If you travel into the great unknown, with little-to-no buildings/interference around, then the Air would do just fine for you.
That said, I still want an Air because I have this nasty tech obsession. But if I'm at home and wanting to fly around, I'm going to always pick the Mavic. It's got better battery life, and it uses an actual radio versus Wi-Fi.
If the Air had OcuSync, I'd be struggling to find (for me) any MAJOR reason to keep the Mavic Pro.