Also, if you manage to cast a Squee, he's a goblin so your rabblemath would need to be updated.
Mandrills is sweet because it can be cast for G, Goyf is sweet because he can become a monster under the right circumstances for 1G. Rabble costs more than both, but provides additional value past his own body. Tasigur is probably just a smaller version of Gurmag Angler in this list as activating his 4 mana ability is not ideally where you want to be. Both Tasigur and Angler require black mana to cast which is somewhat of a downside. If I was going to pick a dude like Tasigur, I'd probably just go with the Angler instead.
The deck may just not have enough surprise value anymore, and as people on MTGO move away from SB options that target shops and PO, the incidental hate towards creature strategies goes up. I have seen a ton more plows, peacekeepers!, and sweepers (pyroclasm, verdict, deluge) recently, and it doesn't take a whole lot to throw off our game plan. Survival decks are going to need to adjust and evolve, and won't be able to bank on people making bad SB decisions and not really understanding how the combos work for long.
I have been having a real hard time against Jeskai Mentor and basically any deck that runs plows and snaps with FoW. I have lost games where I dropped 12 power on board turn 2, and I have been ultimated by a JTMS more than once. Survival at its core is not a control deck, but also lacks the focused aggro plan you might see from a deck like humans or fish. This shoves it into a weird place between combo and aggro/control.