While these can be helpful, I'm not sure how widespread the availability is so you would probably want to provide these glyphs anyway. (I could be wrong here. But I also don't know a good way to assess their availability.) It's also quite nice that you can just type in data with Sparks and get sparklines which isn't possible with the glyphs you mentioned.
Any environment I have that does custom fonts and glyph substitution also has CSS (or similar functionality) which can be used to make them thinner, if desired.
5.2 MB (compressed) is a big package just for some narrower boxes.
5.2 MB is for the whole set, if you are using this font in a project, you will most likely set on one type of font format (.eof, etc.) and one weight (extra-thin, bold.)
The font file ranges from 18Kb to ~600kb, with most in the ~50kb, which is reasonable for the simplicity.
Fair point, but I disagree about even that size being reasonable -- or simple.
There's a million things you can implement as a font. I have yet to see anything I think is a good idea to implement as a font except the defined glyph shapes themselves.