4. Sorcerers must keep learning the same spell at higher levels.
Why does a Sorcerer need to keep relearning Fireball at every level up in order to be able to consistently blast with good damage? Sorcerers already have limited spells known, all this change does is make Wizards more unholy powerful by comparison by effectively making Sorcerers less able to efficiently utilize said spells known.
Metamagic in the past did a fine job of making higher level spell slots more powerful. This just makes wizards stand out as powerhouses more than they already were.I know I've been a broken record about this, but combined with spontaneous heighten, I'm pretty sure this works out to a net buff over PF1. Many spells that get value from heightening used to be a line of spells or have lesser/greater versions (e.g. Invis, Summon). Using spontaneous heighten, you can effectively get nine levels of summon X for the low price of one spell known in the best case, and two or three spells known for the price of one in others.
Spontaneous heighten's two picks are also generally enough to support your main sorc gameplan (e.g. summonbot, fireball bot), negating the restriction on the spells you need most.
When I first read the rules for spontaneous casters I thought the same this as OP. But them I realized that a Sorcerer still has more flexibility than a Wizard during a single day. Lets say they both get into a situation where they need to cast Fireball +3 three times; as long as the sorcerer knows the spell she can cast it three times, while the if the Wizard didn't prepare all three slots with the spell she may only be able to cast it once. If you know what will happen on a given day the Wizard is better, but the Sorcerer is better at handling surprises.