i say conservative because this is me divorcing my strong stance on current summoner and trying to think of things that dont just rework the entire class.
1- charisma impacts you extremely minimally. you have little insentive to throw a attack or save spell/cantrip between your actions being filled with act together, move in tandem, boost eidolon, and attacking with the eidolon. your eidolon face skills are anemic due to poor face attributes, overall there is just...little reason not to even go as far as voluntary flaw to lower charisma down as low as possible to bump con/dex and some other stat you might want more like wisdom just for the initiative or intellect for more skills.
1a- charisma needs a purpose. ideas are a font of some kind. another idea is that the non physical action abilities of eidolons (dragons breath, beasts roar, etc) DC is based off summoner's cha or even using summoner's DC/to hit wich is obviously based off cha. Another idea is some kind of face skill action similar to act together that lets you work in tandem to perform a cha based action and getting a bonus to it. though im not sure if that works. end of the day, charisma needs a purpose.
2- eidolon levels 1-2 only has 16AC, im not sure why they chose to give them expert in unarmored at level 3 and not 1, and im not sure what you'd have to give up.
2a-a simple mundane martial, having caster AC at level 1 kinda hurts. simple solution is just to give them expert from level 1.
3- the summoner is fairly action starved, doing the same thing every single round, with little to no room for various utility actions or activities especially in combat. your turns are largely move in tandem, act together, boost eidolon, re-enforce eidolon, attack with ediolon once or twice. This is not your options, this is largely your round, every round.
3a- the summoner by mechanics alone ends up fairly action use heavy. but boost eidolon seems like an unneccesary upkeep on a class that even with, isnt outshining anyone anyways. I do not see the issue with removing boost eidolon entirely, and moving that bonus to damage into the base eidolon itself, this would allow more options to be used by the summoner such as raise shield, recall knowledge, demoralize, feint, bon mot, etc. would open up a lot of variety for the summoner and i dont see really how it would unbalance anything, let me know if i am wrong here.
a moment of pause- Looking at these 3 proprosed changes. giving charisma an actual purpose, improving eidolon ac to appropriate parody with base martials, and baking boost eidolon into the eidolon itself, would open up the summoner a lot. it might not be my cup of tea, but i dare say it would be worthwhile for someone to play it.
thoughts?