A YouTube video I watched recently claimed that summoners might have been considered a bad class in second edition. However, it doesn't seem like that at a glance - there's opportunities for various creatures and beings to stand by your side, such as a plant monster kinda like Blossomon, a stegosaurus, dragons, and so on. Also they come with a nine level magic collection on top of the Eidolon - and the Eidolon can learn spells too with the correct feats. So you could make a druid like character with lots of magic but their main aspect being able to summon a giant sunflower, as a result of acquiring lots of Druid archetype feats for magic casting and feats related to the Eidolon casting magic themselves. Or you could make a stegosaurus man who summons a powerful stegosaurus that knows a lot about nature and fights for them. Sounds like a cool class to play, but I haven't tried the game much to see how any of this would work in gameplay.
Summoners are not bad. I have a Summoner in my current game and the character meaningfully contributes to damage, scouting, and utility. He tends to burn through his HP quickly with the larger attack exposure of two characters, but that's why they have 10HP per level.
It's a complex class, and the Summoner will never top DPR calculations or out-cast a Sorcerer, but they can flex into martial and caster roles as needed. Wave casting still lets you use staves, so they are even more essential to a Summoner to get the most out of their limited spell slots. Eidolons can also roll their own skill checks, which expands the utility of the party.
The main draw for Summoner is being the peak of all pet classes and it delivers on that fantasy very well. If you want to have a demon or dragon or whatever, this is the class. That the class works without making Summoner as OP as PF1 or completely useless is pretty amazing.
Great comment.
I know you only mentioned DPR as a quick metric here(and I certainly didn't read it as an end all, be all), but if you haven't seen the tweet rant by Michael Sayre (Paizo Design Manager) on it recently, it's a super interesting read.
It makes me like your comment even more.