Damar varnish has one redeeming factor: It can be removed easily with Turpentine.
Water based synthetics can't and they will generally resist really powerful solvents
like Acetone. They don't really 'bond' to oil paint and can sometimes be flaked off
carefully with a blade, but depending on the paint surface they can soak into the weave
and then it's impossible to remove it completely.
I once spent SIX YEARS carefully removing a layer of water based varnish from a 36x24" painting
on canvas. I initially cleaned it which got a lot of muck off but revealed huge brown streaks that
where in the varnish. I flaked it off a bit at a time over that period. Even then there were parts that
I could not get completely varnish free. I ended up having to re-paint sections. Being an artist I did
have an advantage there and the end result was good. I gave the whole thing two coats of retouch
varnish to even out the whole surface and spark it up a bit. Retouch varnish is also removeable with Turps.
The customer was very pleased (and patient) and I accepted a nice garden bench as payment.
I learned a lot though.