Telepresence works fine in the civilian world, where you don't have someone jamming your GPS and comm links. It fails dramatically when you're fighting someone with decent technology. Definitely not a "solved problem." Look at how the Iranians managed to capture an RQ-170...
If the US tries to fight a near-peer opponent like China or Russia, GPS will be jammed, satellites will be either blinded or destroyed, and both UHF and VHF comms will be either jammed or severely degraded. Just recently a US Army General was bitching about how advanced the Russians were with their ECM/ECCM in Ukraine. The Russians are extremely good at this.
The more war goes 'remote control' the more this will cease to be an issue, and this is a dangerous trend precisely because it removes one of the last impediments to scaling up the export of war. As soon as the losses to own troops drop to near zero because all of it is done through robotic means all bets are off, and it does not even require a 'skynet' in order to achieve it. All it takes is some more telepresence and that's pretty much a solved problem at this stage. The difference is that in the air we now have this and for other branches it is still being worked on but within a decade or two we should see robotic infantry.