Off-guard will take some getting used to, but it kinda makes more sense - being flat-footed to a particular creature was always a bit of a weird concept.

The 8 spell schools are very D&D so they have to go in the Remaster. For specialist wizards, they'll instead have actual schools that they studied at, with various themes like the "School of Battle Magic", with a predefined list of spells they specialise in.

You're right, sucking up an action at a minimum from every affected creature is great for a L1 spell, and it can even take an enemy out of a fight on a failed save without having to worry about Incapacitation. It can be GM-dependent though, and in my experience GMs like it when players get creative, so you'll probably have better results if you use some imagination rather than saying "I create an illusion of a bucket on the boss's head" every time.

I'm not sure about vitality for positive though, "vitality damage" doesn't sound to me like something that only affects undead

I guess so, but that's basically saying that if you want to do more things it costs more money. And the Summoner is uniquely good at doing more things because they have effectively more actions than everyone else, but that's certainly not a bad thing.

Not sure what you mean by the "double skill item tax", seeing as eidolons get skill bonuses from the summoner's items.

The scaling on magnetic pinions seems crazy. 12d4 total damage at (character) level 3? 30d4 at character level 9... this makes Inner Radiance Torrent's scaling look slow

Does the GMG really say you should use the PC rules for this? I thought it said you should almost always use the standard creature rules, and that's what APs etc. seem to do. "You can build NPCs just like you would any other creatures. If an NPC should work like they have a class, use the class features and feats of a suitable class to pick abilities, and look at both the class’s proficiencies and ability modifiers to determine how strong the NPC’s statistics should be" from Designing NPCs

Ignition is not a straight nerf from Produce Flame - it now does more damage (and scales faster) when used at melee range