You say Tomori was 'excellent', but how many games did he play for us exactly?. very few. A better player now presumably than when he performed for us in the Championship, but still without Premier League experience really.
This, for me, is the possible problem with any potential loanee, one of commitment, if the going got tough would he go into that crunching tackle? or would he pull out risking injury? I don't believe you can ever be quite sure. After all, Brighton aren't his club, he is contracted to someone...