scaling SpriteFont "should" be okay as long as you have Point on.
however, if you are upsizing the entire game this has many inherent issues.
is your text doing any sort of movement or animated scaling?
I have it on point but spritefont text scaling isn't the main issue. It's more an issue with the text object being blurry by default, inside the browser.
Integer letterbox scaling works fine but I would still prefer non-letterbox scaling. It seems to be impossible to get it pixel perfect with Spritefonts, since that looks even more blurry in comparison with the text object when scaled.