The problem right now is that pretty much none of the arm SoC manufacturers adds what is needed for supporting a full desktop/ laptop experience, that is more than 4 gb of ram, sata3, general purpose pcie lanes and more memory bandwidth for the igpu. Most of the arm chips right now are stuck at 64 bit ddr4 at most, and the ones we have access too ( being libre) have even less bandwidth and are even more limited when it comes to ram.
Just an example, going from single channel to dual channel on an intel igpu increases performance by 20-30%, and that's even on a gpu design much worse than any powervr or mali gpu. AMD's apus are somewhat better in this regard since they have much more advanced memory compression.