The fifth mech in Hack's Command Star was a Pack Hunter.
Given that the Assault Guard were on New Avalon at that time, and that Davion had been buying all the clantech they could get from the Foxes and even building some of their own, I'm not sure it'd need to be more than a company. They could be fielding things like Atlas IIIs, Sagittaires, Nightstars, Sunders, Regents, Mad Cat MkIIs, Templars, Templar IIIs, etc. Sprung on the Dragoons close, where the superior range of clantech matters less, and that'd get ugly fast. Might also contribute to why Hack had Zeta reformed in Rites; firsthand experience facing an elite Assault company will make an impression.
As for Slade, I'd make her at least a Clan Elite. Probably better, given the way she's described in Redemption Rift. I see her as being up there near "best in her generation" level. Maybe Danai Liao could take her one on one in identical mechs. But I doubt more than a handful of warriors alive in 3140 could say that.