Performance and optimization is one of many pieces, but yes, it's a meme to render 500k lines.
That said though, and maybe I didn't say it well in the post, the more performant and optimized your tool is, the less burden you put on developers and users.
Sure you won't review 100k lines, but maybe the diff includes a ton of testing snapshots, or maybe it's a long running feature branch and you need to just quickly jump in and look at a specific change from a specific file. The less the developer or the user needs to think about `how` to render the diff or `how to navigate the diff`, the better we did our job.