I agree completely. Yotsuba is great, but I really hate the childhood friend/crush thing. How could you possibly hold onto feelings for someone after 6 years, especially when you meet them once? I'd like to compare this to the Monogatari Series for a moment, so possible some spoilers.

MONOGATARI SPOILERS:

This 6 year crush thing reminds me a lot of Sengoku Nadeko's feelings for Araragi-kun. She held onto these feelings despite playing with him a couple of times at his house about 6 years prior. She held onto these feelings because it was convenient for her. Now, looking at this from Fuutarou's point of view, Yotsuba was the one that point him on the straight and narrow path, and to put his all into school. If anything, Fuutarou would see Yotsuba as his savior, similar to how Araragi-kun views Hanekawa Tsubasa. What I really liked about the manga up to this point, was that not all the quints were in the running for romance. Itsuki began to truly respect him, and a few chapters ago we had Yotsuba give up on her feelings for Fuutarou.

Miku: Yes I am biased toward her, but reading the manga blind from the beginning made me truly think she was the main heroine in this manga. At nearly every familial problem, her and Nino were almost always there to put them before themselves. From her being ice cold, to being reborn as a confident person. And her confession to Fuutarou when she pointed at all the things she loved...