First and foremost there is absolutely no way that Choji beats Tsunade. Sakura,, however, is quite debatable.
You are underrating the power of the expansion jutsu. The jutsu allows one to become a giant. This increase in the body's expansion comes with increases of muscle mass, size, and weight. As a result, one is easily capable of substantially increasing the impact of their strikes due to:
1. Increased muscle mass meaning an overall stronger body.
2. Inertia that is the combination of pulling forces of gravity, and the speed in which the punch falls down (as it is to note, he's striking down with that height).
Choji was also seen to have adequate mobility while in this mode which also means he is not some slow moving tank, but decently mobile.
Also remember that he had the physical strength to challenge the Gedo Statue which was easily capable of stopping Kitsuchi's mountain sized Earth Wall. Which means hos physical strength is on extreme levels while expanded to butterfly mode.
Finally, remember that Sakura's only known methods for truly attacking is physical strikes (can't see sleep bombs working here). With his ability to leap fair distances (not to mention his own rational intellect) I can't see someone just letting Sakura go punch them in the shins. Sakura can leap high distances, but that doesn't mean it helps. Once in the air evasive maneuvers (what she was trained to do) are impossible meaning she'd have to defend with a punch. Considering their relatively comparable strength levels given evidence stated earlier, I'd say it does nothing, but send Sakura back to the ground when the strikes cancel.
Also remember that Sakura is a medical ninja first and a combat shinobi second. Which means while she will still have skill in combat, she'll notably lack some of the intuition and reactions that combat type shinobi would have in greater quality (since they are typically in combat).
Sakura has great strength, but that doesn't guarantee victory. Remember that her whole style revolves around her ability to control chakra. Even with that, she's notably showed little diversity in Taijutsu other than punches to the ground or average level strikes in combat. So I would conclude that she isn't really a master at Taijutsu, but is only lethal because of her physically enhanced strength.
She can't keep up with people such as Lee because of speed. With Choji, it is due to matching physical strength. The Yin Seal and Katsuyu doesn't automatically guarantee victory. It simply provides Sakura a greater strength to achieve victory.