The underlying code in the libs is c++ just as its c on gnome.
Considering bindings do exist & are fairly well maintained, I would've preferred to have seen them come on-board w/Qt/QML, BUT given political clashes in the past I half-expected that to not happen, sadly.
That of course is only part of the equation, they are way more entrenched in the js side of things, so the upheaval isn't exactly easy...
*in a more coordinated/consolidated way then ever before
1. dynamic typing - performance will be (much) worse than with static typing in most cases
2. runtime compilation - compiler increases memory usage and slows down application especially start-up - code compiled during runtime can't be shared between processes/applications
Youtube is also using Apache written in C and MySQL written in C/C++.
Youtube can add more servers if performance isn't sufficient.
Youtube web application is trivial compared to MySQL.