I may have completely missed the point here but I've gone for James. He can take us to the next level on the pitch and he is capable of magic that Richarlison isn't quite able to do. Richy is our second most important player along with DCL I'd say. Losing Richarlison would set us back as a team and we need to keep him as long as possible but I think James will attract the next level of player as he's a household name and whilst he's mid-prime of his career I think the pull of playing along side him and watching him in training is a big one.
Also the commercial side of things, Richarlison is big in Brazil but James is big in Colombia, Spain, America, etc. Commercially we can progress by being smart and using him correctly. Long term I think we'll benefit more from having James but we should be throwing the kitchen sink at Richarlison to keep him happy and keep him. He's essential for us to keep trying that next step to European football.