TBD as described here is what everyone basically used to do in the olds with SVN (because branches were so hard). PRs are objectively better, just have to complete them on a regular basis. The article conflates PRs with long running branches.
They were also slow because, if memory serves, creating a branch involved creating a logical copy everything (files and history) instead of just tracking the delta using pointers/copy-on-write/whatever-clever-thing locally. It was on the order of tens of minutes in one project I worked on and, needless to say, we stopped doing it. Merging the branch was also (as noted) a headache when this all ran in reverse. Merge conflicts were also much more common, though I can't remember why just now -- presumably because synchronizing changes was equally slow and painful, rebasing was not an option and people couldn't be bothered.
It's hard to emphasize just what a leap forward Git and Mercurial were. In addition to quick and cheap branches, you could also commit changes while working offline! The distributed nature of these tools was also revelatory and is underutilized in the modern age.
I don't remember it being particularly slow on a large code base. It was tricky however, I can't remember the details but it was only ever done if absolutely needed. So, according to this article the bad old days of svn are actually what they want.
