I have parallel lighting systems - a generator light system which is always on, and a battery powered system that I put on the bike when my commute has me riding in the dark more often than not. Strange but I have no issues with the mounting systems of either of the light setups - and they are very different from one another.

The generator headlight is a Supernova E3. The headlight came with a variety of different mounting options, but mine is simply bolted to a braze-on on my fork with an aluminium spacer.
The generator taillight is the Supernova 3 LED affair, which is made to mount to the rear rack, which it does, so long as you have a spacer to allow the wiring to get to where it wants to go.
Both of the supernova lights are mounted via permanent connections where the light is bolted to the bike, and both have been trouble free for over 2 years now.

My battery powered lights are from Dinotte. Both the headlight (200L -LI) and the taillight (140R-LI) mount to the bicycle via O-rings (fancy rubber bands). I was skeptical at first, but years of using this system has made a believer out of me. Simple, robust, versatile.

FWIW, my biggest beef with lights is the lack of availability of generator powered lights which support a flashing mode. There is one on the market which I am aware of, but I am not fond of it.