Question for you:
If you're that Ranger on that boat and you want to protect that little girl and you have the suite of following two abilities (I'm not going to put any numbers to it, just theme), you don't know anything about the HP/abilities of the little girl and the tentacles, how do you make an informed decision:
COVERING FIRE - You buy time for your target to move nearby. Any mook that approaches the target you protect or attacks them in melee is slain.
KILL THE THING - Do a bunch of damage to the big thing!
This assumes that I a) want to protect the little girl (very likely) and b) feel at least vaguely confident I've got enough going for me that turning the Kraken's attention on to myself isn't just going to be suicide. But OK, let's say both a) and b) are true, and proceed.
If you don't know any of following:
(a) the tentacles are classified as mooks
(b) the mook tentacles don't share the monster's HP pool
(c) the little girl's father is actually capable of protecting here (mechanically capable...not just I'm a dad with an oar capable)
(d) how cover rules work at all (if you do COVERING FIRE, she's either moving to her father for protection or taking cover behind the fishing gear)
(e) that the girl is also a mook (therefore guaranteed 1 hit 1 kill vs perhaps having 4 hp and dealing with a tentacle that does 1d6+1 damage so she survives on a 2 or less)
Re d): if I'm an archer I'd assume that in the fiction I'd have an idea of how cover works, though maybe not in a hard-numeric sense. In my game there's also the complication where shooting into melee carries significant risk of hitting the wrong target (mechanically: a rather large to-hit penalty with a miss-by-that-much meaning I hit someone else in the melee), which I-as-archer would already be somewhat aware of; so I'd have to try for tentacles that weren't already engaged with the boaters.
If you know none of that stuff...how are you acting as an informed agent?
I'm not. And that's the point: I shouldn't be - yet.
If I've never seen a Kraken before, I have to go by trial and error. Here, if I want to start with covering fire I might put one shot into a tentacle and one into the body and see how the Kraken reacts; meanwhile yelling up a storm in order to attract the attention of all involved and in hopes of drawing the Kraken away from the boat. If my one shot knocks off a tentacle then I'm on to something, and can focus on picking off tentacles until the boaters are safe; while if my tentacle shot does nothing but the body shot makes it shudder then I know to focus on the body and just hope the boaters can hold out long enough.
In either case I can yell my findings to the man in the boat, if he hasn't already reached the same conclusions. Conversely, if he finds after a round or two that the tentacles come off with ease he might yell the same to me. (somewhere along the line he might also let me know he thinks he can hold the Kraken off for a moment, but that's probably all)
The one additional piece of information I'd ask from you-as-DM, as I don't recall seeing it noted (though it might have been), is how fast my raft moves; i.e. how long would it take me to get into melee range were I to paddle instead of shoot. If I could get there within ten seconds or so I'd have a very sticky decision to make - to paddle or to shoot for the first round - but if I was a minute's paddling away then shooting would really be my only option and hope the Kraken came to me.
How are you navigating that decision-point? In the menu of possible moves you can make based on inferences or meta-inferences (eg how HPs work or how genre tropes should impact play), there are plenty of ways this could go wrong.
Of course there are, and that's the point: in the fiction there's also lots of ways this could go wrong, and I don't at all mind having "it goes wrong" as a possible - maybe even probable - result in a scene like this.
If you don't have those crucial mechanical inputs (tentacles are mooks and as long as you hit they're donezo and you've bought time for the father/little girl/you to get to the raft), how are you not mostly flying blind?
Thing is, I am - and should be! - largely flying blind to begin with other than the obvious fact that those two in the boat are in a world o' trouble if I don't help out - and maybe even if I do. I learn some of the mechanics in soft form (e.g. the tentacles come off easily, the man in the boat knows one end of a sword from the other, the little girl's good at staying out of the way, etc.) on the fly as the fight progresses, just like my PC would in the fiction; but I never learn the hard-numeric mechanics.
The agency-arresting prospects become significant and many/most decision-point become fraught with potential EFF ME AND THE LITTLE GIRL outcomes.
Exactly as expected, only I don't feel my agency has been arrested in the slightest.
I neither expect nor want, in a scene like this, any sort of guarantee that whatever I do to begin with will be the right thing; as I've no way of knowing what the "right thing" is until I've had a chance for some trial and error. Hey, maybe I get lucky and get it right the first time. Maybe not, and eventually all that's left are some rowboat splinters and a stuffed doll floating on the lake. Them's the breaks.
But assuming I've any system mastery at all, giving me all the mechanics pretty much tells me the answer "
Here's the optimal solution!" before I've even had a chance to ask the question. I find no fun in that.