Almost had a TPK last night in the Pathfinder 2e beginner box

So, I've been running the PF2E beginner box, which is like a tutorial adventure, for a group of 5 people (we play as long as at least 3 show up). The players had the option of playing any of the pregen "iconic" characters for Pathfinder. So far, we've had a fighter, witch, monk, swashbuckler, and summoner. Of those, only the witch has any sort of healing, and the witch player couldn't make our session last night.

The players went into this room that is meant to be like an optional miniboss (but there isn't really a way for them to have known that). The miniboss is this fire elemental rat that is supposed to teach you how "persistent damage" works. It's a very tough fight, and the elemental has a lot of defensive options like a cloud of smoke around it. Eventually the rat killed two party members (the swashbuckler and the monk), and one more (the fighter) went unconscious but didn't die. The last player (summoner) got chipped down to like 3 HP but was able to drag the fighter out of the fight to safety.

I think it was a good learning opportunity for the players that you need to be tactical and work together in PF2e, since they basically just all tried to attack the rat in melee. It also shows the value of having support characters in the party.

Going forward we are going to complete the beginner box, the two players who lost their PCs are going to play new pregens (bard and investigator). I'm hoping the players don't get too disillusioned with PF2e because it is very difficult at times.

I'd love to hear other Pathfinder GMs' thoughts. I'm still new, so it's possible I was doing something wrong, but I think I ran that fight the way it's meant to be run.