It could be that a critical hit can still take out your Tarlak even at 4-80, so using a banner or giving him monk emblems to make it more sturdy is always a good idea.
Tarlak same as Miki are almost a must have for high scores against those kind of titans, so it is totally worth the tonics 
No Miki for me unfortunately. Evelyn is begging for the tonics and she seems to be the overwhelming consensus for them before Tarlak but part of me wants to go for titan damage first to increase my 4* AM chances. I’d just hate to skip her over for Tarlak and then find out that those tonics didn’t make a difference for his survivability.