90+% tackle efficiency 4 season in a row, the only season it was below 90% was his first, the stats don't support your observations.
Always a Bulldog
Call me an optimist but these types of signings can be beneficial to juniors (not hindering) they're considerably cheaper than a Haas type middle and ultimately do the 1st priority tasks, yardage, hopefully no nonsense, couple cheeky offloads, and just do the job(see stats). They seem professional (I'm mostly referring to Twal as I see him on field and interviews more but Keppie isn't a slouch).
Junior props want these contracts, game time.
All along they're training alongside, opposing sessions too. They want to know, they need to see, they need to outdo these players to CONSISTENTLY play in the NRL. On the training paddock the juniors that are trying to crack in and establish themselves in the NRL look at these types of players.
So even if these props eventually get outdone by a couple juniors, it's not a large chunk of salary cap 'flopped', they'd always be ready to cover back in for the squad rotation as long as training's fine. Buzz and critics will call them flops after a couple years but there's plenty of indirect benefits out of these types of signings.
Plus the Bulldogs fold usually (used to) bring the best out of these types of players. I can see these two, bar injuries, enjoying Bulldogs compared to Tiger's and Manly.
win-win