Evan Fournier on paper, looks like a good fit to be that veteran wing that is part of the core rotation but maybe off the bench (or maybe starting). I don't know his game well enough to be able to have an opinion on his defense or other non-box score contributions.
As to Aaron Gordon, he has always been a player of interest but he is really a swing, hybrid wing-PF but doesn't shoot the 3 as well as Theis although is more athletic of course. Theis and Gordon are the same height (6'-8"), we probably get more rebounding and better 3pt shooting from Theis, more versatility from Gordon. I am not sure we need Gordon for what he costs.