20 hours in a sous vide is too long. The meat starts to get mealy at that length. I'd say 15 hours max. I try to stay around 8 to 12.
The first "sear" is really just browning the meat, like you'd do for stew meat, since the meat is going to continue cooking in its own juices in the sous vide tub.The grilling takes care of the second sear. I have done a second sear on roasts that I have done sous vide for long cooks of 20-24 hours, and not grilled or smoked after. Rolled in butter and oil pan searing, or brushed on and broiled to get it nice on the outside.
130F is a pretty common temp for venison roast. 135 if you like it medium. Temp has a big effect on texture. Especially with fish and seafood. Lobster tails you will see at 130-135, but I prefer the texture that 145-150 results in.
It sounds like extra work, but not really. The prep and finish work are pretty easy, and not very time consuming.
The first "sear" is really just browning the meat, like you'd do for stew meat, since the meat is going to continue cooking in its own juices in the sous vide tub.