There are a few ships that have abilities that don't help themselves, but help other ships around them. Some entire ships are pretty much designed to be a support role.

Lando

Chewbakka + DtF

All named HWK -290s

All named shuttles

Dutch Vander

Garven Dreis

Any one with Swarm Tactics

Any one with Squad Leader

But the kings of support ships IMO are:

Howelrunner

Captain Jonus

And they are not the kings just because of the obvious offensive potential for their abilities.

They are great because their support ability isn't limited to one ship, but to all ships in range.

I keep trying to build a Support Shuttle List, but each time I decide that I would rather have Howelrunner or Jonus so they can boost the whole squad, not just one other ship.

I keep trying to build a support HWK-290 list, but then I end up wishing the Rebels had something like the great Imperial pilots.

There are a few ships that have abilities that don't help themselves, but help other ships around them. Some entire ships are pretty much designed to be a support role.

Lando

Chewbakka + DtF

All named HWK -290s

All named shuttles

Dutch Vander

Garven Dreis

Any one with Swarm Tactics

Any one with Squad Leader

But the kings of support ships IMO are:

Howelrunner

Captain Jonus

And they are not the kings just because of the obvious offensive potential for their abilities.

They are great because their support ability isn't limited to one ship, but to all ships in range.

I keep trying to build a Support Shuttle List, but each time I decide that I would rather have Howelrunner or Jonus so they can boost the whole squad, not just one other ship.

I keep trying to build a support HWK-290 list, but then I end up wishing the Rebels had something like the great Imperial pilots.

The trick with a HWK list is to make sure you have enough room for at least four ships. There's always the temptation to load up on upgrades and/or expensive pilots (e.g. Wedge + Jan), but then you're even more vulnerable than you normally would be with a three ship list. Here's a sample list that's worked well for me so far:

23 "Dutch" Vander

5 Ion Cannon Turret

1 R2 Astromech

21 Kyle Katarn

4 Blaster Turret

3 Moldy Crow

1 Nien Nunb

21 Rookie Pilot x2

I keep trying to build a support HWK-290 list, but then I end up wishing the Rebels had something like the great Imperial pilots.

I think you're missing the primary difference between Rebel and Imperial methods...

A Imperial pilot that only helps 1 other ship per turn is a lot less effective, because you generally have more imperial ships then rebel ships on the table.

Jan Ors only giving out 1 extra attack die can actually increase the power of 1/3rd of the whole list, as opposed to 1/4th or 1/6th of the list.

The trick with a HWK list is to make sure you have enough room for at least four ships. There's always the temptation to load up on upgrades and/or expensive pilots (e.g. Wedge + Jan), but then you're even more vulnerable than you normally would be with a three ship list. Here's a sample list that's worked well for me so far:

23 "Dutch" Vander

5 Ion Cannon Turret

1 R2 Astromech

21 Kyle Katarn

4 Blaster Turret

3 Moldy Crow

1 Nien Nunb

21 Rookie Pilot x2

So that is basically 29 points for 1 extra focus a turn and blaster turret. I think I would just prefer to take Wedge. Sure Wedge doesn't help anyone else, but he is awesome on his own.

If you're looking for a good build for the HWK, here's the one I've had the most success with.

Wedge Antilles, R2 Astromech PtL

Luke Skywalker, R2-D2 Dtf

Jan Ors, Ion Cannon Turret, Chewbacca

Anything with DTF is a decent support ship, it's just better support on ships with Shields or Chewie.

As for Howl and Jonas being "Kings/Queen" of support due to the "limitless" number of units they effect. You need to remember there is a large difference in Tactics between the Alliance and the Empire.

the Rebels are more "Quality over Quantity" meaning they're going to have less ships in general so while having a pilot that can support a "limitless" number it would be overbearing since it would increase the ships by a much higher effect.

the Empire favors "Quantity is Quality" which is why outside of large based ships and the Advance there are no shields to be found. Since shields are a quality item. With such a high number of fragile ships it makes sense to have a Limitless Support ship since Single Action Support ships will have a tough time buffing large groups especially if they're unique.

the Empire also follows a "head of the snake" model with it's Quantity strategy.

-----

Since you wanted a Shuttle Support List have you tried this:

The KING of "support" ships is Biggs. With him in the mix his compatriots are sitting pretty. His support may not be the "boost you up" kind but it is the "keep going, I'll hold them off" kind which allows other ships to do what they came to do.

Chewbacca is NOT a support ship although DtF turns ANY ship into a support ship.