It is just a machine that came to you with a problem & you have not yet found what that problem is. Once the problem is found & rectified there is no reason for it not to be reliable.
That this problem has not been sorted by your initial diagnoses doesn't mean that those diagnoses were the wrong course of action to take, just that they did not get to the root of the problem & another course of action requires formulating - with the possibility that will not get to the root of the problem either. Deep seated problems can take a lot of finding - you just need the right mindset to keep going, and possibly a dose of luck !
I would be tempted to go right back to basics on the ignition first.
Was the orientation dowel for the dynamo rotor fitted to the crankshaft.
Did the points cam fit it's orientation cutout & was the cam in good condition.
Did you fit new points ? If so, did you clean the points faces, as some have a protective coating. If not, were they assembled correctly (moving contact properly insulated). Could you get the correct points gap AND correct timing point ? Is there only one place during 360 degrees crank rotation where the points open (mis-aligned or bent crank)?
Your Velleman ignition mod is an unproven item. As a test, rig up a temporary ignition circuit completely separate from the bike wiring - you only need a ground wire from battery negative to dynamo ground, a power wire from the battery positive to the coil & a link wire from the coil to the points (with the condensor re-instated). Note that the coil contacts are numbered & are connection sensitive.
Such a circuit will bypass all the bike electrics & should provide reliable sparks. If it still doesn't run, plug out & drop some premix down the plug hole - I have used the little screw-off sediment bowl on the fuel to do this. Plug back in & even with a duff carb it should run briefly. By way of an experiment some years ago I had an ETZ 251 "running" without a carb or exhaust fitted by just dribbling a bit of fuel into the inlet port & regulating the engine speed with the ignition switch !
Don't let it beat you - you seem to have been able to sort the various issues with your 612 Bullet with perseverance & this is no different.
I have NOS points, used condensors that I have a tester to check out and a collection of carbs that I am happy to post down to help you get to the bottom of this.
It is only a machine - it has not got it in for you - you can fix it. It might just take a bit more time than you had initially thought.