Yeah like I said, this sort of thing never used to bother me, but lately it seems kind of self-defeating and obnoxious.
About the do-over, I dunno. I've been in situations where a DM was perfectly happy to tank their campaign by murdering the party with an overpowered encounter, and that always left a bad taste in my mouth.
This time, it kind of was our own fault, for backing a bad play, so I'm not sure what I would have done if I was the DM. I do this sort of thing in my own games though, let the players see that monsters out of their league don't stop existing just because they're low level (and vice versa). Usually I'll have an encounter at some point that is just out of their reach, like sighting a purple worm burrowing close to the surface, or a dragon in flight- if they want to go for it, they'll be rewarded, but if they die, I happily tell them I don't feel guilty at all, as it was their choice, lol.
Though as I often tell DM's who come to me for advice, you have to be careful; if there's a result you don't want to happen (TPK), you shouldn't put the option on the table in the first place. And here, I think he was going for a cool "let the party know there are dangerous things out there" moment, and never really thought we'd try to go for it.
The thing is, it's a 5e game, and Hill Giant's are that high in CR so maybe it could have happened if we'd had a real plan, and set up some kind of traps or something. It was just so spontaneous that nobody was ready for it. That my friend insisted on dying to the Giant rather than admit he made the wrong play, and his complaints afterwards, made me really question if I've been enabling him by putting up with his nonsense.
His characters can be fun to play with, but moments like these leave me scratching my head. For example, saying you don't know anything about magic or monsters is one thing, but he never even asked, which is what I always do. If the DM tells me I know nothing, so be it, but I feel that characters living in a fantastic world should have some clues about things.
Sometimes his characters attempting creative ways to solve encounters is fun, like when we found an old storeroom with bags of flour- the DM didn't realize how flammable flour was. Or the time we found a barrel of "smoke powder".
But trying to make firebombs using torches and lamp oil in battle seemed a bit excessive, when you could set something like that up in advance, if the DM was on board. And refusing to use combat cantrips just strikes me as strange. Sure I get it, some people don't like Wizards having a "magic crossbow" and using magic to solve all their problems, even combat.
But at the same time, I don't miss the "throw darts" days one bit.
Anyways, I guess there might be more going on here than I've considered. If his actions come from a dislike of modern gaming, or feeling that he'd be a better DM, those are toxic behaviors and need to be addressed.
Thing is, we tried going back to 2e, I could tell the other people in my group weren't having any fun, so if that's what he thinks we should be doing, he's going to have to get used to the idea that I'm the only other person who is willing to play. For years he's boycotted WotC D&D editions, and I was hoping that exposing him to 5e and get him playing again would get him to change his opinion, but he's still griping about 3e getting rid of Thac0, and it's been 23 years now!