Similar or worse job to pets? The only thing that Koumei is worse at priming is an aoe secondary with encumber, which is what you should be running anyway.
Max number of unique status is 13 (actually 14 or 15, but Koumei/encumber can't apply void or tau) which means Koumei's 4 has a 57% chance to put every status on enemies in LoS. You get crit chance, crit damage, armor strip, and extra damage if you aren't relying on status damage, which won't be factored into the math here. A melee weapon with multiplicative CO like the Nepheri or Corufell with 13 statuses hit for an extra 1040% multiplicative damage. Granted a primary or secondary doesn't get the same bonkers percentage, but an extra 80% or 120% respectively from galvanized mods starts to get scale really well with crit. Secondaries also have Secondary Shiver that triggers CO which at max cold stacks, again only a 1 or 4 away, is another 450% multiplicative on certain guns.
I will reiterate that most people have bad weapons and don't know how to use them. Koumei is not a caster frame, she is a gun platform that lets you hit in the millions by casting a single ability allowing you to bring more utility/damage into your missions instead of wasting weapons/companion spots on priming. Take off all your mods and arcanes on Koumei, take everything off a Stalhta except serration and vital sense, cast your 4 and shoot some stuff. Put galvanized aptitude on the Stalhta and repeat the process. Then do it with a Corufell if you want to see some really big numbers.