They are winning major companies over and selling more and more workstation and professional graphic cards. In fact quarter on quarter and year on year they are significantly up. They cards are general compute powerhouses that can run a huge variety of computational work really fast. Even Nvidia's Volta is too weak across a wide range of computational workloads. It might beat AMD offerings in few workloads by a big margin, but it losses across a wide range.
Furthermore AMD can lower prices and stay competitive that way. I would definitely buy a Vega 56 over the 1070 or 1660ti at the same price. RX 580 8GB has been as low as $200, RX 570 as low as $160, these are tremendous value. GTX 1060 6GB has not moved bellow $250, apart from very few specific sales and promotions or low cost single slot cards from partners like Evga.
But AMD actually have the lead over Nvidia, they will release 7nm graphic cards somewhere around June/July and will have the process lead for over 6 months, likely 9 months before Nvidia can come with a new architecture.
In the meantime they are competitive with their price drops, again who would buy a GTX 1060 or 1660ti over a RX 580 or Vega 56, especially since the RX 580 can be had for $200-220 Heck with sales and promotions you can end up buying a RX 580 for as low as $180, that is insane. RIGHT NOW there are 2 sales on newegg from powercolor and XFX selling their 580 8GB for $180 and $190.
RX 570 goes for as low as $140 on newegg and comes with 2 new games with it. Right now there are 3 sales on newegg.