I feel sorry for anyone who still holds this self deprecating mindset after their first few sessions &⁵e designed to cement that mindset. I've seen this attitude in players occasionally in past editions, but it was generally limited to extremely new players approaching it with the mindset of a video game or similar competitive game where they need act as the first last and only mind on the island of every man for himself. I'm those past editions those extremely new players sometimes proactively looked at the risks where they quickly learned the depths of how far teamwork & collaboration in games like d&d early on. Other times those players had to look into that abyss of risk retroactively after things had gone sideways. Sideways can be anything from one or more PCs almost dying or using far more resources than reasonable to compensate for poor choices all the way to one or more players scolding them from the bully pulpit of a dead PC. In both subsets of players the players had to communicate their strengths and weaknesses so they could discuss how the party can better work together with a higher degree of teamwork & efficacy.
Now in 5e I see that self deprecating attitude in a significant plurality if not majority of new players and any efforts by anyone at the table to communicate in ways once needed to crack the ice are rebuffed as an offensive overstep to be ignored. That dismissal is reinforced by 5e's extreme lack of risk at anything because everyone quickly learns that there is no risk of every man for himself Unless the GM resorts to fiat and adversarial adventure design that can squarely aim the blame for failure at the GM. Even if someone at the table looks at the failure and tries to discuss what the PCs could have done differently, wotc has firmly entrenched the idea that it doesn't matter because their meat computer cheated to unfairly cause that failure just as the bolded bit of your post asserted before listing off scenarios where you were helpless unless someone had been prepared for those obvious party weaknesses with buffs debuffs battlefield control coordination and so on that would have previously been temporary combat avoidance and so on built up in the party teamwork muscles session after session.
When that sort of party teamwork structure never develops, it causes the problem where instead of seeing the Trainwreck coming early enough to dial it up to 11 so the party can seize the W the party just tips from "everything is fine" till immediately crashing into the L with no toolset developed to right the ship because they've convinced themselves they are powerless and avoided considering anything that might get suggest otherwise. After all, 5e has taken great pains to mislead you into thinking that your choice to put all of the party's eggs into shock &awe has nothing to do with the loss, it's that GM who designed the encounter who owns 100% of the responsibility.
I...genuinely do not know what you are saying with "that self deprecating attitude."
And when I'm talking about these things, I'm genuinely not kidding when I say this is the second or third combat of
the entire campaign. Not "we went several levels and did a bunch of adventures." I'm talking about things where the group hadn't even actually been together long enough to even know what the other characters could DO yet. And yet we were having bandits jump us in the middle of a critically-needed short rest after the third combat of the entire game, so the DM denied us any healing (because we hadn't
finished the short rest, see) and then had a squad of bandits roll in. At which point, we TPK'd (except, as noted, the Rogue who managed to run away).
Having already had literally the second combat of the game end in a "we barely survived" and my character specifically would have unavoidably died without the DM actively (and begrudgingly) allowing a
remove curse, and then the third combat being
again "we barely survived," only to get jumped by bandits after
only the second short rest we'd ever taken in that campaign, yeah. I was done. I was thoroughly demoralized and had no desire to continue playing in that game, despite the other people there being friends.
I am, if you'll pardon the pun,
deadly serious when I say that I have, on at least two (possibly three) occasions, been put in a situation where we got a full or near-full party wipe
at or before second level, for literally no other reason than that we decided to go to where the adventure pointed us. In the first two of those cases, both times the group had no more money than a 1st-level character starts with, so each group had no meaningful ability to acquire new tools. Each group had had fewer than four fights (three in one case, two in the other) before the TPK fight, meaning we'd had nowhere near enough time to learn how to work together as useful teamwork. In both cases, any spell slots we had were mostly depleted because, again, we'd already had a rough combat recently.
There
literally wasn't anything we could do. We were taking the adventure at face value, going to a place we were supposed to go, and stumbling into a combat at that place. On two different occasions, with
completely unrelated groups (one a group of friends, the other a group of strangers), this resulted in a TPK (or effectively one.)
This has nothing to do with underestimating my own capabilities (which I guess is maybe what you were meaning?), and everything to do with
there literally just weren't any options we could have used.