I think my biggest difference between something being a companion and another character is the INT factor. Animal companions need to be handled and trained. And in combat they shouldn't know to much about tactics and such like an eidolon would.
Their masters can easily direct them. And they get access to the tricks, which can make them far more useful early-on than an eidolon. A Druid can practically automatically start with an AC trained as a mount, while an eidolon must spend an evolution on it.
There are a lot of trade offs that make an animal companion almost even with an eidolon as it looks they tried to keep them about the same. I say they are a second character due mainly to the INT factor. So they stay around even as they progress but in combat an eidolon gets the advantage as it can think for itself and knows some tactics.
I'm curious as to where you get the notion animals don't use/know tactics. Have you ever watched a wolf-focused nature program? They clearly demonstrate flanking, hit-and-run and attrition-based tactics. Prowling lions also make the tactical decision to run down the weak or sick. Animals, particularly predatory ones (which most of the Animal Companions are), are quite intelligent hunters.
Druids and Summoners will probably not be alike in combat unless they are built the same way. A summoner gets abilities a druid doesn't and vice versa. So they come out even as they should and you have to play the tactics you decided on when you made the character.
Eh, far from it... Druids get their higher-level spells faster, get Wild Shape (providing a bonus to AC and stats, while retaining casting with a feat), and end up with 9th-level spells. Summoner gets some class features pertaining to the eidolon and the Summon SLA, which eventually becomes Gate-able, and that's the most-powerful ability he has. Gate is fairly potent, but using it to summon a creature in battle carries a cost well beyond just using the SLA.
What I am trying to say is you could build a summon spamming Summoner just as easily as a Druid could (with the added bonus of less casting time) based on your feat and spell selections.
Again, far from it. My Summon SLA grants me less time spent summoning and longer duration, sure, but I can only have 1 use of it active (note: I'm going by baseline Summoner, not the ACFs). The Druid can just cast and cast and cast... The Summoner can learn Summon Monster as a Spell Known, but I say again, it eats one of the precious few Spells Known and then I'm on the same page for casting as a Druid - same time, same duration - and I never can get Summon Monster 9 on my Spells Known.
The question becomes what type of character do you wish to play and then which class is better for the chosen type. One class should be a little better than others in an area of combat style - You could play a greatsword wielding Wizard who fights like a meatshield (mage armor, shield, heroism, enlarge, falselife) but a fighter is much (much) better at that role.
Oh I understand there's trade-offs, believe me. What I'm saying is the "trade-offs" leave Summoner in the dust compared to the classes most-capable of doing what he does without the eidolon. I think I've already pointed out how much Druid kicks Summoner ass (and still can kick Fighter ass, just not as badly as it did in 3.5). Wizards seem easier to keep up with, but they get Scrolls-making and their vast spells known, making them hard to keep up with, too. And let's not forget 9th-level Spells.
See, a Summoner's spells, even with a high CHA (which mine is not), top off at 6th-level Spells. His big guns are much easier to negate/avoid because their DC will be 3 points lower. So his big, powerful spells are spent on largely... well, a collection of oddball spells that don't really seem to fit the class all that well, IMO.
My thing is eidolons vs companions and familiars. Maybe for me it has always been that the latter two always seem add ons that are used here and there by the character and the eidolon seems to be a separate entity from the character.
HM
I think considering familiars and eidolons should be left in completely separate categories. A Sor/Wiz does not send the familiar into combat. Eidolons have much more in common with animal companions, except for one thing. The Druid does not
need the animal companion to remain a potent class. The Summoner
needs the eidolon to be a potent class, particularly in an AP as savage as WotBS.
And Walking Dad pointed out something important - the stats I rolled. Which, by the way, came out very odd, IMO. As they did for pretty much everyone... 7d6 and an 11 is the result?
I had not expected Barrik to become a combatant. I expected to be a support-caster with a front-line pet. Instead, I got rolls saying 'go fight', and couldn't really change a thing about them. So I tweaked my concept a bit to go with the stats I had received and went where I was intending to go in the first place.
Personally, coming from a view with a lot of entrenchment in 3.5 mechanics, I think the Summoner is a fairly good class. It's about on-par with a Bard without the stigma attached to the performer. But it is still easily outshone by Cleric, Wizard and especially Druid. Even a decent Sorcerer could show-up a Summoner, if that Summoner doesn't have the eidolon.
