Indeed, in my opinion OTA-13 is a monstrous update, perhaps the most consistent one, which required a phenomenal amount of work, all this done with very limited means: we have to be aware of this, and even more so if we don't do the analysis and programming work !
So especially a big thank you to all the developers who continue to bother and tear their hair out for this OTA 13 ! The 'grail' will be I think when https://github.com/ubports/qtwebengine-opensource-src-packaging/pull/30 will be merged.