What benefits can we get from the use of GFDM?
In a system where subcarrier crosstalk is not defined by how well the parties are synchronized, synchronization can might more easily be implemented. Whether that really compensates for the more complex filtering structure is up to research or even questionable.

Point is that you can actually, in math and simulation bring down OOBE with GFDM, not even considering different comparison bases for the number of subcarriers:

Consider this: The pulse shape of a single OFDM subcarrier is inherently a sinc. Hence, the first side lobes of the outermost carriers can only be $\approx13$ dB lower than the desired signal, and will continue periodically, whereas such a statement cannot be universally made for GFDM.