This again sounds like people who have never actually piloted the Som'er summon factory and have only seen the perfect storm of its use. It isn't as simple as it looks even if your opponent patiently sits back and allows it to function at full capacity. The activation order alone screws most people.
As far as the Slop Haulers healing, well let's just say Som'er manages to summon a full compliment of 3 Bayou Gremlins in a single activation (that cost 9 SS for the 3 Bayou Gremlin's that are the targets, plus 2 SS for the Family Tree Upgrade, and another 5 SS for the Slop Haler, total of 16 SS, and the Bayou's can't activate until after both Som'er and the Slop Hauler have gone)...
To make this work it will cost at least 1 card plus a 6+ card and Som'er's 0 Action to guaranty the required suit for Get Your Bro (Via Do It Like Dis!) ,3 cards with a value of 8+ to succeed with the summons, and then 4 cards of 6+ value to heal the injured to max wounds. You have also done nothing else with your master (His entire activation was spent summoning and guarantying the suit), tied down the Slop Hauler (who can only do something else if he chooses to go Reckless a the cost of 1 Wound but has to remain close to Som'er to provide healing again next turn) and can really do nothing else with 2-3 of the Bayou Gremlin's because if they move outside of 4 inches from Som'er they can't be used for summoning next turn.
...that leaves 2 Bayou Gremlin's still at 2 Wds. The rest of the 4 Bayou Gremlin's will have between 2 and 4 wounds (Let's assume average flips which returns them to full wounds).
Which Bayou's does the player choose to leave in the Back Field? Does the player risk moving the wounded ones from the back field or use the healthy ones (for the moment anyway)?
Likely the player is going to choose to leave the wounded ones (who are also probably Slow due to summoning, why use Slow ones when you will want to run the healthy non-slow ones drunk and reckless so they are OP'd). So what happens now? Som'er has 2 injured Bayou Gremlin's near him that he hopes will heal before his next activation so he can summon off of them. He also likely has 3-4 "healthy" Bayou Gremlin's (that 4th one will be slowed due to summoning) primed to dash up field Drunk and Reckless. End result 4 Bayou Gremlin's upfield at half wounds or less (because of Drunk and Reckless usage otherwise the Bayou Gremlin's are crap right?), 2-3 in the backfield (near Som'er for next turns summoning, 2 of whom are likely to be at 2 Wounds).
Let's say your opponent doesn't or can't take advantage of the situation to kill your Bayou Gremlin's upfield. Next turn you run the summon engine again. Net result is not going to be the same. The Slop hauler now has to go before Som'er in order to heal those 2 injured Bayou Gremlin's in the back field that he will use to summon the next wave. If Som'er decides to summon a full compliment then he will have 6 Bayou Gremlin's in the back field that are all going to be at half wounds with no way to heal them until the next time the Slop Hauler can activate next turn. That also means that they can't go Drunk and Reckless because they won't have the wounds to live thru it.
We also still have the problem of healing those Bayou Gremlin's we ran upfield last turn who are likely injured from running Drunk and Reckless.
We could use those Lightning Bugs at a cost of 5 SS (So now the total is 21 SS to make this work because you are going to either two of them or a Slop hauler and a Lightning Bug to have any kind of board coverage) but of course to really maximize the healing we really want to use that neat little trigger on their Magic Blasty Stick. Let's assume they are in the 8 inch bubble for Som'er's Do It Like Dis! (to provide the ) They still need to succeed with an attack to make it work. Do we target one of our Bayou Gremlins or an enemy model that happens to be within 3" of all the models that need healing? Targeting one of your Bayou Gremlins will result in it dying on any success (any damage flip bar the Black Joker from the Magic Blasty Stick kills a Bayou that went Drunk and Reckless before it can be healed from the trigger). Targeting an enemy model risks failure (so no healing) and requires favorable positioning of the enemy model to be sure to heal everyone that needs it. Again let's hope your opponent is obligingly positioning his models to aid the summon factory but not hamper it.
While a lot of this is theoretical "in a vacuum" example, it demonstrates the fragility of the Summon Factory even when everything goes right and how it just isn't sustainable long term without a lot of effort and costs (and even then there are diminishing returns). It also requires your opponent to be unable to dissect the support required to make it function. Protecting that key Slop Hauler is very difficult, particularly given the access to models that can engage it first turn From the Shadows. After that, you have to worry about protecting those squishy Bayou Gremlins that are required for Som'er to summon. This is not that easy once they have sustained the damage from summoning. Again From the Shadows deployment can easily dissect the required models though Lure can wreak havoc as well due to the tight positioning constraints. Lightning Bugs can somewhat replace the Slop Hauler's but they aren't that much more durable or easy to protect (and of course their healing isn't free either even with a "healthy" friendly target to trigger off of).
Now don't get me wrong, I do agree that the Lightning Bug's triggered healing could probably go from 2 to 1, but it doesn't come with out risks (using it could result in healing your opponents models as well).
Now a lot of this can catch a player off guard the first few times they see it, especially if the perfect storm of sequence, position, and card draws occur; however, once they have seen it, it doesn't tend to work anywhere near as well. That Slop Hauler (or Lightning Bugs) and injured Bayou's don't tend to last very long. My players have become fairly adept at removing the healers early, forcing me to transition to one of Som'er's other play styles mid game (this is why I really favor building a crew that can do this with minimal effort).
Not trying to sound condescending (though it's the internet so who knows how it will sound) but the Summon Factory is not a viable play style for more than a turn or two (and if it isn't running at "full power" then it is much less of an issue and even easier to deal with). Having run it for years now, it just really isn't a consistent path to victory, particularly when you consider that a third to almost half of your hiring points are spent just trying to give yourself the best chance of making it work (and hoping that those damn From the Shadows models don't show up to ruin your day).
Like I said, I can think of a lot of other summoners who are a significant;y larger problem than Som'er.