Yeah, hes pretty strong right now. But being able to take map control does not = duelist. Otherwise sova, viper and skye, etc. would all be duelists, they take the most map control with the wall, dart, and dog/flash. Duelists do not take map control, they use the map control that the support agents invest their abilities to, trying to set up duelists for kills. Can you use chamber as a quasi-duelist? Yes, you can, similar to alot of other agents entrying like skye or kayo. Is chamber anywhere near as good as the other duelists purely for taking space and entrying? No, his tp cooldown is too long, and the range is too short. Yes, he can slowly take ground over the course of a round or use his tp to swing an agressive angle, but it is no where near the level of jett/raze, or even reyna and neon. yoru is in his own niche.
He exerts a lot of pressure by being there, but that doesn't make him a duelist. the duelist role is generally to entry for your team and clear site first, while taking initial duels because most kits are set up to give an advantage to the duelist. Chamber's kit doesnt really give him an advantage when executing site, only for initial angles or holding space and aggressive angles. Yes, you want your duelists on agressive angles, not because of the ROLE, but because most of their kits are set up to give them the advantage. Chamber's kit also gives him an advantage when holding angles, but that doesn't make him a duelist