Is D&D still relevant to the market/hobby? Sure. Despite all the others that have come out over the decades, D&D remains the best-selling, most-played, and most-imitated RPG of all time. If you add in its direct imitators (Pathfinder/Starfinder, OSR, every "OGL d20 System" product, etc.), I would be shocked if D&D doesn't still account for an absolute majority of all RPG purchases, player numbers, and play hours.
Is D&D still relevant to me personally? Nah, not really, other than as a lingua franca of RPG discussions. There are so many other systems that I like better that I have a hard time seeing D&D ever coming in as a game I regularly play again. (And, since you mentioned it in the OP: No, GURPS is not one of those systems.)