I’ve had slam crit for 15k before, its not a bad filler ability.
WW still does the WW only damage to the primary target even with FoB talented. So with FoB talented, the primary target takes a slam + the WW damage.
Plus tactician has a higher chance to proc the more rage you spend from an ability.
Realistically though, either way, you most likely end up with the same overall number of tactician procs. Just you can either gamble with the higher chance from WW, or have more samples to fish from by using slam on ST.