Last time I tried it, ungoogled chromium had some issues with yubikeys (see https://ungoogled-software.github.io/ungoogled-chromium-wiki/faq#how-to-get-fido-u2f-security-keys-to-work-in-google-sign-in) which I don’t think have been fixed yet. That was enough to be a deal breaker for me.
do yubikeys suck as much as it looks like they suck?
Without knowing why you think they suck, it’s hard to say. I like having unphishable uncopyable credentials, and it irritates me that they aren’t more widely supported. On my desktop or laptop, they’re less irritating than TOTP, for example, which is neither unphishable nor uncopyable but much more widely used.
whereas passwords that will always be copy-pasted are 128 characters
Whilst there isn’t really such a thing as “too secure”, it is the case that things like passwords are not infinitely scaleable. Something like yescrypt produces 256-bit hashes (iirc) so there’s simply no space to squish all that extra entropy you’re providing into the output… it might not be any more secure than a password a quarter of its length (or less!).
128 bits of entropy is already impractical to brute force, even if you ignore the fact that modern password hashes like yescrypt and argon2 are particularly challenging to attack even if your password has low entropy.
The solokey v2 and the nitrokey v3 (I think) have some firmware upgradability, but they're not as capable as a yubikey (the last time I checked I couldn't use either of them to unlock a keepassxc password vault, for example). Whilst it would be a right hassle to deal with a lost device, I generally lock my accounts with a main key and two spares that get stored safely and make a note in my password database of which accounts can use which keys so there's little risk of locking myself out of anything, and I can get a list of sites to visit to revoke credentials from. In any case, the minor inconvenience is a good tradeoff for me, given the significant security guarantees the keys offer over other authentication mechanisms.
But also, "added complexity" is just a thing with two factor authentication, and most of my use of U2F keys involves less effort than unlocking my phone, then unlocking my TOTP application, then searching for the account and site I'm trying to unlock, then waiting for the timer to reset because I can't authenticate before the current code expires, etc.
Beats me! I just use off-the-shelf entropy calculators and hope they're right. They mostly seem to agree that ~128 bits of entropy from a 10-word (70-85-ish characters) passphrase from the EFF large wordlist, or ~24 characters from uppercase/lowercase/numeric. Both might be reasonably considered overkill, if you can be sure that the thing that's hashing the password is using a modern algorithm (which often you can't, sadly).
I also dislike unreasonably long passwords because more modestly-sized ones can be typed out manually when needs be, or even read over the phone in an emergency. I wouldn't fancy doing that with 128 character passwords! You may of course never need to do those things, but I've needed to do both, at work and otherwise.