Missed the playtest due to medical mishap and miscellaneous eff-ery,but I had a few thoughts tangential to references made and my feelings on the matter.
The Summoner 'fantasy' has always been difficult for me to pin down aside from knowing what I personally like. The concept of course ties bac, for me,to Final Fantasy IV (US 2) and Rydoa, who could cast other magic as well, but the Call spell ability was HER thing. The lore tying the life force of the summoner/caller to the caster was more used for drama with her mother, but never seemed to overly affect her.
Seeing the ability as manifest across other games in the franchise kept me interested through all its permutations - such as when, in FFVI/US3 the summons were espers and one of the main characters, as a half-esper, filled the concept space for what I would want in a Synthesist. Overall, the summons remained, more or less, like those Volatile spells from the playtest, flavored as the individual incarnations we've known and loved...up until X.
FFX for me was, unless I am misremembering, where I first encountered the eidolon nomenclature...and the newer, persisting behaviors that underlined the tabletop counterpart. I dug the concept, even if it was still time-limited in game.
Since then, of course, there's been 2 Final Fantasy MMOs, several spin-offs, and at least one competitor that took on the concept in a similar way - World of WarCraft. The warlock was already mentioned as a 'pet' class, but I think that some further examination of the conceit is merited.
In WoW, the overall class was the same across the boards...in theory. In execution the specs/paths filled massively different niches even within the damage dealing role. Destruction was a direct 'nuker' whose attacks were empowered by certain debuffs deployed, with their demons serving more or less as an attack accessory (and for a time you could learn an ability that let you ritually sacrifice your demon servant to gain a buff and one of its abilities! ). Affliction was all damage over time, all the time, culminating in obscene damage output...so long as you could keep several proverbial plates spinning at once. This also made for a common tactical shift of using the weakest summon, because it passively improved you spell damage and did direct damage for you while your Damage over Time spells ramped up.
Demonology changed the most over time, but was consistently the path/specialization the most benefitted player and summon alike as they could heal the demons more at less personal cost as well as empower the pair with ease,on top of getting access to special, stronger demons.
By comparison, in FFXIV, the summoner no longer had the arsenal of incarnate elemental beings to choose from - no, the lore of the setting instead granted you access to 3 specific entities...or rather, fun-sized fractional emulations of their powers. Which is rather what the playtest Summoner feels like. In FFXIV it comes down to DoT spells, special resource cooldowns, and whether you want pure offensive melee damage (Ifrit), melee damage with a defensive shield (Titan), or ranged damage (Garuda). Their abilities are flavored around their elements so it's fire, earth, or wind - or GTFO.
The one detail I give credit for that isn't the 60/70/80 abilities, is that under the hood is a pair of specific spells that are actually Egi (your Eidolon/Eikon-lite) commands...and given the design philosophy of 2E and the summoner's concept space, I would rather like for the request for buffing and support spells focused on the eidolon to include the option, given the sharing of souls and spiritual energies, of using the castle's hypothetical spell slots to fuel magical abilities OF the eidolon.
Such an ability would add extra significant for those who focus on their eidolon rather than summoning other monsters. Conversely, calling monsters for hit and run/disperse could be hilarious if the summoner gets conjuration/summoning, rather than just the latter half.
And while I know people have already gone all-in on the Pokémon inference, I can't help but think that a more Digimon-esque approach, focusing on a base eidolon with multiple configurations as levels increase, might make for an interesting archetype or later class feat. "Lantern! By our pact, battle evolve into Trumpet!" And the angel-emulating eidolon's configuration changes to match the more powerful entity,entity, long as there's enough evolution points...and after battle/expiry the form reverts back to fun sized,and the pool is drained until next rest.