I obviously wasn’t there to see the game play out
@Retreater, however I have Lost Colony and I am half way through running that campaign.
First off - this isn’t an introductory adventure. It isn’t described as an introductory adventure. It’s intended for Seasoned characters, which is an unwritten assumption and therefore could obviously be more clear. But if you start the game with people who have never played the system before (in real terms, given you group’s reported history) they might find things tricky. You say the players are using the archetypes, which are seasoned, so in theory up to the job from a stats perspective - more on that later.
Lost Colony is a slightly strange campaign setup. As a somewhat lawless frontier location with advanced tech people who go looking for trouble tend to wear body armour. So humanoid enemies are often Toughness 9(4). It’s actually worse than that if you read the rules - this is a bit of a rushed product in my opinion and most of those armours should actually have ballistic protection added on so would be 13(4) versus bullets. I my campaign I play this as Kevlar body armour and people rarely wearing helmets so head shots have become very common, or they close to melee where the ballistic protection would not apply.
In terms of the opening there are a few things I would comment on.
First, the second group of combatants in the fight are local militia fighting against the insurgents. So the system expects the GM to hand those off to the players to run. I appreciate that this makes it potentially tricker for the players but Extras are pretty easy to run. I just printed out their stats (smaller than a post-it note) and told them you are controlling these four guys. In your group I would have given the NPCs to your two more ‘engaged’ players to run, either two each our four to one of them.
You mention that they were struggling with high rate-of-fire. Looking at the Archetypes and assuming you used them without modification then only one character has a RoF weapon - the ex EXFOR trooper. They have an edge to eliminate the penalty when shooting with RoF so would be rolling four d8 and one d6 looking for 4+ to hit. They should have been getting lots of hits unless the enemy were turtled up in cover. Their gun does 2d8 damage so the average result should shake enemies, too. Using bennies to turn unlucky results into average results is a good way of looking at how to use them, and situations like the EXFOR soldier shooting and missing badly would be prime examples of that.
Two more things.
First, the insurgents are not there to be killed, they are there to set the scene. The ‘good’ outcome of the adventure is that the party take out at least half of them and they surrender. But even if they escape the party has still come together and is in contact with the BDF who will give them the next part of the adventure as a mission. The way I would play the fight is that the insurgents are doing a fighting withdrawal, and if the fight gets drawn out they try to flee. I might even call it at that point and give all the players a Bennie as a reward for driving them off. The key thing here is that fights do not have to be about killing all the opposition. In many cases, the opposition will be intelligent and seek to run away when the odds turn against them. If they are animalistic enemies then they are also likely to flee if they discover ’lunch’ is a lot more tricky to catch than they thought. Fighting to the death is a common approach for many groups but it really doesn’t need to be that way in Savage Worlds where you don’t get XP for killing enemies and so there is no sense of ‘cheating the game’ if you ‘win’ by causing a route.
Finally, all combats are kind of intended to be a big deal in Savage Worlds. Any attack could result in death! So while I agree that an introductory fight should be relatively quick and easy to help the players get their heads around the system and understand the risks / chances of success that their characters are facing - this wasn’t designed as an introductory fight. If I was using it as an introductory fight then I would have gone more on getting the PCs to run the NPC militia to get the basics of attack and damage while their own PCs lives were not at risk. In future, if you are facing a filler combat, use the Dangerous Quick Encounter rules instead to limit the chance of TPK while keeping the in-world fight and risk of some attrition.
Savage Worlds isn’t a perfect game, and Lost Colony is one of the weaker books in the line though still a lot of fun. The weakness manifests in slightly weaker editing, and no physical bookmarks which most of their new books have sewn in. But I haven’t personally experienced a car-crash of the scale you describe. I know your group have challenges with even reading and remembering the rules, but that is a problem for pretty much any system I would think?