I would be wary of adding more muni sinks into Overwatch because their cost, impact and ease of use might outweigh the Goliath's high-risk high-reward proposition.
Thematically I feel that the leFH fits the commander better than the Sturmtiger and I'm not sure a Sturmtiger would be a more useful replacement.
I think a Pak-40 could fit this commander.
