I agree with Black Adder... weapon upgrades and stats are nice, but not required.
I played 2 antag games last night. Played as Konstantin with a basic Lv0 Tsiklon, which is STILL glitched, and I beat a mixed level group (some higher, some lower) and was accused of cheating right after (LOL). Played as Hive with a Lv10 forged MM-6C (her default gun) and wrecked another mixed level team that included a Doldren 12 levels higher than me. It was their Lycus that killed me the most, and he was under my level. Skill, playstyle, and character choice can overcome raw stats. CQC will always be deadly for someone involved, grabs always kill, shooting someone into wounded state to finish them is also going to always be effective.