Alright finished my testing for now. Just like predicted SMilk is very strong, probably the 2nd strongest iron DPS now. She still does a little less than my Raven, but once the investment is even she'll outperform her.
Also like I predicted her best playstyle is fast shooting while maintaining the pierce with a full charge shot every 6sec and you also gotta do a longer full charge after every one of her bursts to regain the S1 and S2 buffs. Her gameplay feels fairly awkward and needs getting used to, but she performs significantly better than on auto or manual full charging only. These tests were also just on the shooting range boss so you can expect a significant improvement on her performance for any boss that lets her pierce parts like the upcoming Mother Whale SR.