We direct radar let downs all the time but I think you mean conduct a radar letdown as a co-pilot using a weather radar not actually designed for the purpose and not cleared for IMC use below 1000'.
Crab, I don't think you have seen or used these inferior radars or you might not have made this comment. I have used them and they are more than capable of closing a boat to 0.25 of a mile. I was quite surprised how good they are. Having the whole picture in front of you is also very handy. They are pretty good at mapping the coast as well. No doubt there is better kit available but this is SAR not finding a coke can in the middle of the Atlantic (something I have also see and done). If you need to get closer, you probably shouldn't be there.