From that list it surely has to be Alfie Hewett - two singles grand slam wins and three doubles grand slam wins, finalist in two of the other three tournaments, 3 other singles titles and world #1.
O.
His problem will be that most people won't have even heard of him - difficult to amass votes if the people voting need to be told who you are and then what you have done as part of the SPOTY process before they'd vote for you.
All of the others have significant name recognition, which, let's be honest, is an absolute pre-requisite for a potential winner.
I agree that there isn't a clear front runner and it is a little bit B-list, with a couple of folk on the shortlist on the basis of career achievements rather than in-year achievements.
I have no issue with SPOTY going with career achievements particularly in a year when there isn't a really compelling stand-out in-year achievement. I'm biased, but I'd go for Stuart Broad - second highest test wickets by a fast bowler of all time (and that's of all test playing nations, not just England) plus finishing his batting career by hitting a 6 and his bowling career by taking the final wicket in the final test of an ashes series against Australia to win the match.