You'd kill Reg faster if you had shamblers.
Seriously now: your build and some experiments made me re-think the 'no early Shamblers' approach a bit. They do add a lot of dps, especially early on AND after you max out GS. I still prefer to invest my skill points as scarcely as possible, if playing a long evenly skilled game (where Tribute would make a bigger impact than any other skill in this game, so I'd like to tech it ASAP, at 15, not at unrealistic 19-20). If you get Shamblers, it's stupid not to invest into Mulch as well. If you invest into Mulch... Well, bye-bye Tribute and new shiny Bulwark. However, if I see the game is going very well for the team, and we are on the offensive, I spend my saved points on Shamblers to get as much dps as possible.