Spawn rate isn't the problem it's spawn zone. So like when you find an area they spawn like 50 will be there but when looking for them you may have to fly a good distance to find them. Needs to be a code or something to make them spawn further from each other. Also I have never seen the nether mobs and I have tried multiple times. Set up and afk over night to see if I could get some to spawn and I couldn't.
Tip: sometimes going to the area your looking for and waiting in a tree can get them to spawn