It’s supposed to be challenging, I always thought that was the point as you did harder content. I don’t know but I’ve been healing for a long time and in my experience the difficulty of healing is not so much different than before.
If anything has really changed it’s the players and expectations. There seems a general desire to get through everything as fast as possible. Obviously M+ has a lot to do with that, but in all aspects of the game there is a trend of burning through content at ever increasing rates. There is little appetite for struggle or mistakes and many players will quit even after one wipe yet alone several.
Finding a healer can be hard. But it’s always been that way, even a long time ago. Healers and tanks have always had a higher value than dps. The usual solutions offered to this are joining a guild/community or making friends with healers. Barring that you’re just going to have to wait in line.