@daichinobakudan—
Graphics in manga are typically far more pictographic than those in western sequential art. Forms of characters morph to convey ideas. (I don't happen to
like that aspect, but my preferences are presently beside the point.) Suzu is small to present her as more vulerable; perhaps deliberately or perhaps as an unintended side-effect, she is made more appealing to much of the audience.
Suzu is in fact well in the lead in the implied race amongst these girls.