You answered your own question
9950X3D will be the flagship (best) CPU for overall use. Hugely faster in productivity (applications) than the 9800X3D, thanks to double the cores. Faster in some games, same speed in the rest.
Also likely to overclock better, since AMD bin the dies and give the best performing dies for the 9950X3D.
9950X3D also better value, since you're getting double the CPU (double the cores) without a doubling of price, assuming 9950X3D has the £749 launch price of the 7750X3D.
Many have paid £550+ for a 8 core 9800X3D, a 16 core for ~ £200 more is a better deal to many.