I don't think so. Why would it be a concern? It's not like the web rendering engine will "phone home" under your nose or something...
1. Way better vim binding support. Especially that the vim mode doesn't break when the extensions aren't loaded (ie a page fails to load or dev tools are focused or on settings pages)
2. Way more scriptable and customizable.(luakit is much more mature in this regard)
Love to hear more about exactly what is more scriptable and customizable.
The user scripts (not to be confused with Greasemonkey-like userscripts) gives me all the scriptability I need. What could more could I do with luakit?
User scripts only run when a page is loaded afaik.
User scripts (again, in the qutebrowser sense, not greasemonkey as it seems you're thinking about) is launched when the user wants them to launch. See more details here: https://qutebrowser.org/doc/userscripts.html
ps: first start feels great
Plus it was really easy to write simple quick scripts for it without the overhead of web extensions.
The main reason to use it is the Vim support is rock solid, instead of a hack on top of existing behaviour.