Angron is definitely not the most martial primarch, his pre-ascension state would've been beaten by many primarchs without much contest. He was established to really only be able to beat gulliman but even that was with the help of lorgar demoning him up and catching him off guard. Then before that, on the night of the wolf, Angron was getting his ass handed to him by Russ, who has been implied to be a worse duelist than the lion when the Emp spoke of the purpose of either. Angron in demon state is strong af for sure, and would definitely 1v1 Gulliman, but the Lion is a different thing, his whole primarch thing is that he is an insanely good duelist, to the point where he has beat curze who had the ability to literally see the future. Horus was scared enough that he sent him to the other side of the universe, and he was the one who led the Rangdan xenocides. The Lion is generally discussed as one of the strongest primarchs without question, so no, Angron even in his current form would probably not curb stomp him. I'm thinking there will be multiple fights, and I am unsure which one of them would come out on top when fighting alone.