Interestingly I have the exact opposite experience, I've reported issues both in the WebCodecs specification and the Chromium implementation, in all cases they were fixed within weeks. Simply though reports on public bug trackers and it wasn't really a major issue in any instance.
> Another issue I ran into that I just remembered is animating text on canvas. It's basically impossible to get pixel-perfect anti-aliased text animation using a canvas. I would have to dig up the exact details but it was something to do with how browsers handle sub-pixel positioning for canvas text, so there was always some jitter when animating. This coupled with the aforementioned WebCodecs issues led me to conclude that professional-quality video rendering is not currently possible in the browser environment. Aliasing, jitter and artifacts are immediately perceptible and are the type of thing that users have zero tolerance for (speaking from experience).
We're doing SOTA quality video rendering with WebCodecs + Chromium with millions of videos produced daily, or near SOTA if you consider subpixel AA a requirement for text. In general for pixel perfection of text, especially across different browsers and operating systems, you can't just use text elements in DOM or in canvas context, instead text needs to be rasterized to vector shapes and rendered as such. Honestly not sure about potential jittering when animating text, but we've never had any complaints about anything regarding text animations and users are very often comparing our video exports with videos produced in Adobe AE or similar.