I don't think the league is lacking dominant bigs so much as there are teams built around dominant bigs like there used to be. There are a lot of good Centers in the league now and Ayton didn't become #2 or even top 5 simply by entering the league. Each conference has 3-4 potential All-Star Centers right now and then a tier below that of 3-4 Centers that are quite good C's but not quite All-Stars.
The top tier of All-Star Centers would contain Gobert, Karl-Anthony Towns, and Jokic. In the East the top tier consists of Embiid, Drummond, Vucevic, and Marc Gasol.
The 2nd tier Centers around the league, which is where Ayton is currently, is comprised of guys like Nurkic, Capela, Steven Adams, Jonas Valanciunas, Cousins, DeAndre Jordan, Myles Turner, Brook Lopez, Horford, and Enes Kanter.
That's a lot of good to great bigs. Like I said, I'd put Ayton in the 2nd tier right now and hopefully he becomes a perennial all-star but he has a number of guys to surpass to be that. I think he has the talent but the idea there is a lack of quality bigs is something that I don't think is true.