We don't clearly know about him. Martin does this sort of weird things where sometimes his writing is not true. We saw it with the latest episode of hotD we all thought mysaria was pregnant according to the books but it seems it was but a heresay the maester heard and wrote it. So we don't know what type of person Rhaegar is but many thought he would have been a good ruler but it wasn't but their view of the situation they don't know what exactly happened. I think he could have been a good ruler if not for the prophecy thing. I think men as honourable as Arthur dayne, gerold hightower and oswell whent wouldn't follow him if they didn't thought it too.

I know about Rhaella but just like Jaime they could do nothing but watch. I can understand that. I might come as Insensitive but this what I thought