The thing is people act like Suigetsu can keep on liquefying himself, it uses chakra and Suigetsu isn’t known to have large reserves so Sakura can keep punching but can he keep liquefying? Not to mention she has water affinity and can to a degree control some water so he isn’t suffocating her either.
Suigetsu has actually been shown to have very large chakra reserves.
He had enough to transform into his monter fish form, which was able to push back Gyuki and tanked his tailed beast ball, and this was after already having been involved in a drawn out battle.
Secondly, Killer Bee confirmed that Samehada takes up to six tails worth of chakra at a time, having riduced him from a seven tailed version one state to a one tailed version one state.
Suigetsu however has so much chakra that he didn't even feel the effect of Samehada taking his chakra when Kisame slashed through him until Kisame pointed it out five minutes later.
Manga proves that Suigetsu is a chakra beast, in fact, all of team Hawk are monsters in that regard. Jugo had ridiculous chakra on his own and moreso since he gathers nature energy continuously, Karin is an Uzumaki so of course she's a chakra tank and she did take down a bijuu level Shinsu Senju, and Sasuke of course also has great chakra.
Remember also that Juugo at the summit was in a riduced twelve year old form (after healing Sasuke against Killer Bee), yet he almost matched the Raikage in chakra, speed, and power. In his full grown form one has to wonder how that fight would have panned out.
Anyway I'm getting off track, point is, you're wrong about Suigetsu, he has a tremendous amount of chakra. His weakness for lightning style however is a problem. He would fair much better if he wielded Samehada or the Hiramekai. (block lightning/vibrator blade with the chakra blade Hiramekai).
