How does IV80 sounds for you all?

I think it definitely usable but ttar is a raid boss you can get a better one tomorrow.

Iv 0 is usable, just not optimal.

Any Tyranitar is useable. A larger point many have made here, Tyranitars are still available in raids, try that way first. Today I felt I needed another one...have 3 at level 30. After a double Moltres raid, I rallied a group of 7 to drive 3 miles to raid a Tyranitar. We beat it, most of us caught it. Mine was 2073cp at level 20, 89%, 15attack. b/FB...TMed to b/c. It'll take some dust and candy to get it to 30, but a lot easier than buying 9 incubators and walking to get the original 125 candies to make a Tyranitar. Not fair in relation to rural players, but I feel similarly disadvantaged compared to players in dense downtown areas.

Just powered up one of 80%iv... Of course, usable. At level 30, I'd say the difference between perfect and 80% of same moveset are almost negligible.

Whatever it is, it needs to be close to L30 to be usable. It takes 66 candies to get from L20 to L30. An 80% is not worth that plus the 125 candies it takes to evolve, since you are likely to hatch a better one.
On the other hand, if you catch an 80% wild Larvatar at L30, it is worth evolving to save the 66 candies for power up.

I would evolve it were the level high enough and immediately usable. I would not spend dust on it.

Yes. I power up Pokemon with IVs as low as 67, as long as they have good movesets.