None of those strike me as preposterous. To me its more about what tier of player your in, and to me Tatum is somewhere in that 10-20 Tier with the potential for upward mobility. Personally i'd have him more 12-15 but the 10-20 range is all pretty similar level of player.
I'd have Kemba where he is in SI based of pure talent in a vacuum, but probably closer to his ESPN rank in terms of actual on court production this year given the knee issue.