They were already legends before the 90s. But they had songs on the radio in the 90s. Aretha Franklin - A Rose is still a Rose came out in 98. Stevie Wonder For Your Love - 95 - he won two Grammys for it., Prince had several top 10 billboard songs alone, not including R&B charts. Obviously their greatest work was before the 90s. They might have been past their peaks ( but they still had decent song that didn't chart well) but R&B wasn't necessary on a decline in the 90s, because of that. But its personal preference. I listen to 70s , 80s, and 90s all together, each era had a different style of R&B. Some music was more soulful, some had live instruments, some used DAWs ( even Stevie Wonder used them) , but the feeling was still there throughout the 90s, Imo. The 90s had some hiphop influence, but it wasn't as obvious as it was in the 2000s.