You're not using enough PTFE tape or it's being overtightened, use gas tape, 6-8 turns wound opposite to the thread to ensure it doesn't unravel while tightening and just tighten it enough to seal and don't wind it all the way in. Those taps don't look as they are designed for bath filling though. As they are 1/2" then you may find they will not increase the flow enough.To fit on to this existing thread, but it leaks at 3/4 end, even with PTFE and as tight as I can get it.
If you want 3/4" wall mounted taps then you will need to pay a premium.