yep! bitcoin is literally anti-efficient

Correct, the difficulty (official term) adjusts every ~14 days so that the average time between blocks remains 10 minutes or so. But the rewards of each block is constant within each halving period. So you can outcompete other miners by purchasing better hardware, or getting cheaper power, but it's a slow grinding process.

The halvening instantly halves the block reward, so everything is twice as expensive per bitcoin. If your margins are thin now, they're even thinner after the halvening.

Here's a chart of the difficulty over time (no endorsement of blockchain.com, this is public info):

https://www.blockchain.com/explorer/charts/difficulty

Yeah, and even worse for bitcoin, when all the miner competitors fold (and the block difficulty goes down) the old mining equipment still exists. So this could be cheaply gotten by bad(er) faith people who want to fuck with the mining (for which you wouldn't need to run the rigs constantly, or in the case of some bad faith miners they are not really bound that much by budgets). Of course the utility of this is a bit low, as most you can do (I think) is disrupt parts of network for a while (which could open up some financial fraud things) but still, if I was a state looking to disrupt crypto because some of my enemies are using it, getting large mining capacity at pennies for the dollar would be a potential move (I don't think states actually see crypto at large as a threat to anything btw, which if I was a diehard gold standard anti state cypherpunk crypto bro would make me worry).

I do wonder if the price of mining will eventually fall so low that only state backed miners or fraudulent miners can still mine (mining is easy if you don't pay for your power).