how did you remove the mesa bits?
if you used dpkg to do it it might have helpfully uninstalled some of the Qt5 packages too.
The weird thing on my system is I cant find how I fixed it…
My pi3 with OSMC is my primary dev system for hyperion so it definitely needed it resolved - even with a quick hack!
I remember hacking the mediacenter script at one point to force the library search path but it looks like its now the default.
I wonder if the installation order is important for how the library search path ends up. It will have been months since qt5 was installed, but OSMC get updated monthly
EDIT: found an old post of mine on here:
This modification is currently not on my system