You guys should've been aware that Baby Princess Peach already appeared in one of those Yoshi's Island series before, like Yoshi's Island DS. Especially Mario & Luigi Partners In Time. So it's not really THAT pointless to add her in. The metal and baby characters for certain characters are like, "Oh you wanna play a light weighted Mario? Play as Baby Mario!" and "You wanna play as the heavy weighted Mario? Play as METAL MARIO!". Heck it'd be interesting to see if that physics logic can ALSO work on the next Sonic & SEGA All Stars Racing game just by adding Classic Sonic, Classic Tails, Rosy The Rascal (AKA Classic Amy), Classic Knuckles & Metal Sonic (Or just Classic Metal Sonic even though they look the same except height).
A Blue Hedgehog who runs at the speed of sound...
A genderless Nightmaren who flies in Nightopia...
A Shooting Star who flies around the Valdi System...
A human boy who uses his legendary chicken suit...
A Rudie skater who sprays Graffiti around the city...
Together...They'll be unstoppable...