You are correct in assuming that a gradient from blue to 100% with no other color will look somewhat washed out at the black end, and also throughout the gradient.
A rich black, however, is NOT 100% of each color. It is impossible to print that color with offset (too much total ink on the plates) and can be challenging even digitally.
A rich cool black is 70C 35M 40Y 100K. A gradient between that and your blue should yield a nice result.
Also, a gradient with your blue at one end and your blue + 100% black at the other end would also work well. It will a rich “blue black.”