The processes used for FPGA are VERY competitive with GPUs. Stratix 10 is at 14nm, for example. Stratix V was built using 28 nm process and that was at least 5 years ago - on par or exceed NVidia.

You can fuse more operations into DSP using FPGA and/or you can perform less operations per FLOP. One example is to avoid rounding and packing/unpacking when creating deep pipelines for floating point processes.