he's an 8 year old who everyone in wano counts on to be the next shogun. King ordered the entire beast pirates crew to go after momo earlier in the arc because that would rob the samurai in the alliance of their purpose. Imagine the stress an 8 year old would suffer from being the center of attention in a brutal war of incredibly high stakes. Momo additionally sacrificed 20 years of his biological lifespan so his people wouldnt die from kaido's madness. What exactly do you want an 8 year old to do? Perhaps you'd prefer a badass caricature?
Tama showed up even though she didn't have to and is using her DF in a better fashion, so maybe she should be shogun.