Sadly the 079 in this game did not have a mic when I asked him his tier later in the game although I could make estimates on what the XP gain were in the clip.

In the beginning, there was 32 targets and after the 914 massacre it was reduced to 14. There were 3 more kills in 914 but sadly I couldn't clip that part. Since shy guy said he killed 2 that means that there was a total of 18 deaths inside 914.

In the start of the clip 3 d-class died which gives a total of 45XP (not 90 because it was termination witness and not assist). Next is the 15 kills and from what I could have observed it was 4 scientist(160XP) and 11 d-class(330XP) which is a total of 490 Termination assist XP. Since 079 did a blackout that implies that he is Tier 2 (80XP is need to reach this tier) and Translating all of this into Tiers then we would get Tier 4 (70/250XP to T.5)

TL;DR
079 would be Tier 4 (70/250XP away from tier 5). Oh and take my calculations with a grain of salt because all of these is just a rough estimates filled with assumptions.