I'd like to do a full post of my own to kind of reinforce my opinion on this, but let me tell you, I feel the sorcerer is immensely underpowered and it has a lot to do with them not knowing enough spells to keep up with the wizard, cleric,and bard. You get a couple f power jumps over other classes around 8th level, but it seems like the wrong way to approach class balance, building a game where you play for months on end with one person having a huge advantage over your other players. Like I said,I promise I can prove this- I've looked over every feat and feature of the Sor vs Wiz and they're so close to being equal if the Sorcerer just learned 1 spell per level and bloodlines were just completely reconsidered, especially bow that signature skills mean nothing. The Wizard is given so many ways to cheat around their prepared casting restriction and while the sorcerer does get some pretty mean damage bonuses earlier than wizard, it's just a meme... It puts your class in this watertight box that says "this is what you do" and then you're an idiot if you don't take overpowering spell as soon as you get level 8. This heightening feat honestly comes across more as a bandaid fix to a severe limitation than a feature of the class.
Likewise, we can't do anything to the sorcerer that makes it so overpowered, like (not to target anyone, but...) give them the ability to heighten spells above the level they can cast already, especially twice per day, because that's effectively putting the sorcerer 2 levels ahead of everyone else in the most significant category of their build.
A facelift on bloodlines and 1 spell known per level should be enough to bring the sorcerer to par with other casters.