Granted, not everyone might see them as good, and a lot of people’s opinion probably comes from other people talking about them rather than experimenting with them in a real game.
Without going into details, and save for the few early levels, during which you might have seen a few skunks being conjured to great effect, a top-level summoning slot brings up a creature between 4 and 5 levels below the party.
Due to how encounter math works, a creature of this level is counted as between 0 and 10 XP in the rules for building an encounter as its chances to hit are too low to matter against the player (-5 to hit against +5 to all defense at a minimum, often more from proficiency upgrades).
Of course, that’s for abilities targeting defenses, surely I just have to pick things that don’t target defenses or satisfy myself with spawning an annoying flanking/body blocking buddy? This is correct, some very select support-oriented monsters, like the Satyr or, in an undead campaign, the Deathless Acolyte can give an amazing boost for their level in a vacuum; but that’s before considering what truly seals this pan of the game for me
It’s woefully action intensive for the caster. A good way to see it is to say that you’re spending 3 actions to slow 1 yourself in order to add a level -5, stunned 1 monster on your side of the board, and if the support action of a Satyr might feel pretty good, is it really compared to other uses of 1 action for the caster, like using a composition cantrip, an appropriate metamagic, or using a well-chosen skill action like bon mot or demoralize? and that’s excluding the initial 3 action opportunity cost you could have spent on a more potent spell
In short, there is a reason why level -5 creatures don’t count in the encounter budget, and while a well-chosen one might impact the fight positively, 2 of its actions are almost never going to be better than 1 action of a creature 5 levels higher;
Of course, that doesn’t mean the spell is useless, out of combat in the blood lord adventure, for example, a single cast at 4th level of animate dead can be used by the Wizard to heal everyone for 20 + 3 x (2d8+16) to distribute on the most injured in a minute with a deathless acolyte; that’s amazing, and notably way more than the 0 a wizard would be able to provide otherwise. Similarly, if you know something is booby-trapped and you don’t want to risk your rogue, a Crawling Hand will happily eat and “disarm” it for the party for the cheap price of a 1st level spell.
Summoning was specifically defanged in combat, probably as a design concern about minion spam that was prevalent in previous editions, so just… don’t use it in combat and demoralize/bon mot every turn instead, you’ll be doing more good for your party
yeah, there might always be that summon in that case that has this ability doing the right thing, but you already have spells as a toolbox, and it’s rare you can’t do whatever you wanted your minion to do better yourself. It goes without saying that counting on anything with an accuracy is basically moot with the 10 points to hit vs defense differential, and very few summonable creature have good guaranteed support (a lot of them were either moved to uncommon or errata’d, like the Bone Croupier recently). To me it’s rather clear that Paizo doesn’t want us to use those strong accuracy-less effect through creatures and we’re only left with a few non-disruptive scraps
I’m however completely unconvinced about soaking damage, for that to happen it needs to be threatening, and, excluding some specific situations as mentioned above, they aren’t, and are as likely to hit as a player is to crit, which, on PL+1 and up, is probably only on nat 20s. If your GM sinks an attack into that, he’s saving you from yourself by removing your sustain tax. In fact, Illusory Object is a better body block since it’s way waaayyy larger, is a 2nd level spell at most, doesn’t require sustain and also requires at least an action to disbelieve which uses your spell DC as a “AC” instead of the AC of a PL-5 creature.