I think we have too many minis that give multiple attacks

Extra: Flobi
Darth krayt
Grievous sotj
Vader lotf
Gen windu
Imp gov tarkin
Jedi exile

Double: Gen aayla secura
Gen grievous sup comm.
Geonisian overseer
Nym
Old rep commander
Star destroyer officer
Tion medon
Vong subaltern

Twin: Whorm loathsome
Grievous dac
Rebel capt

The characters that give Extra are usually expensive or their CE is restrictive (tarkin).

The characters that give Double are usually either expensive or too restrictive (YV subaltern).

The Twin givers are the most useful to make old characters useful.

All may be aggravating, but they do not make the whole squad. It really depends on the rest of the squad. I have made many squads that do not use any of these and have beaten squads containing one or more of these. It just takes confidence and practice.

Also some of those have specific requirements to be met to give those extra attacks. Other than a specialty squad how many use Tion? I don't see alot of those being used regularly in competitions.

It's necessary to have these CEs in a world where everyone and their dog has Evade.

You forgot to list General Grievous, Scourge of the Jedi as a character that grants Extra Attack.

I find that while those commander effects seem to show up a lot, it's usually with a high cost character, (and/or) restrictive, and usually there's only one character per faction that gives such a commander effect.
I also find that those CEs are very good for new players to start learning how to make effective squads. Where better to start than with a single good unique commander that grants extra attacks and build around it? At least, that's how I started.

Well then that would make the factions more even. Isn't that a good thing?

Well, the original designer (Rob) did a great job of building the game, and now we have a new designer (Peter) who's designs will show up in the Dark Times set. Let's see what he comes up with - I personally am looking forward to what is to come.

Now who in this list is really considered all that broken and/or dangerous? Two Seps can grant Twin as command effects but how often do you see the Rebel Captain breaking squads? Twin is certainly nice especially when combined with the ability to make multiple "normal" attacks but does that break those commanders?

As for all those other commanders who can grant additional attacks how many of them are that strong? You forgot to include the Commando Droid Captian in your list of Double but most of those double granting figures don't see much play outside of the very targetted effects of a few. Of the pieces that just grant an Extra Attack (you left of the GONK Power Droid) most are very expensive pieces with some general limit on their power.

Now as far as I'm concerned the biggest offender in the war of multiple attack is NOT the figures which allow for multiple attacks but those pieces which can MOVE and still make multiple attacks. I really think Greater Mobile Attack is one of the most broken abilities in the game even if you compare it to things like Evade. If a piece has to choose to stand still inorder to use multiple attacks then all those extra attacks carry their own risk as you will need to be exposed for multiple rounds to use the full attack; if you wanted to move you were restricted to one attack (or twin) although mobile allowed you to retreat to cover. GMA breaks that by not only allowing you to move before making all of those attack but it still allows you to retreat once the attacks are made; if GMA just allowed you to move and make multiple attacks or act as MA it would be a lot better in my opinion.

And Evade is necessary in a world where everyone and their dog can move and then kill a piece multiple times their size in one activation.

actually I think both Evade and Twin came out in Bounty Hunters, so neither was first.