I would disagree with that. You’re right that home rentals did exist through sites like HomeAway but my understanding is that Airbnb completely changed peoples’ attitudes and encouraged a large group of people living in metropolitan areas to rent out their homes for the first time. Sites like HomeAway largely consist of secondary/holiday homes.
So in that sense Airbnb did create a new market. They made it possible for people without a second home to earn rental income and made it cheaper for those looking for inexpensive accommodation to stay in cities around the world. That’s certainly what got me onto their platform; the ability to travel to my favourite cities and stay in nice homes for not much more than the cost of a hostel (and in some cases less). Not the fact it was better designed or facilitated online payments.