Meat Loaf’s first two Bat Out of Hell albums were different from anything else going on at the time, but of such quality that rock fans embraced the albums wholeheartedly. It just proves that good music can sell even when the trends aren’t going your way. And that Jim Steinman, the writer of the first two albums, is a genius. The third Bat probably would have gone multi-platinum as well if not for Steinman’s absence.
BTW, I’m 41 and my first experience with Meat Loaf was the 2nd album.
But if you want to understand what the big deal was, it’s not hard to figure out if you listen to them. The songs are epic, the lyrics unique and clever, the production top notch for the time, the hooks quite solid, the vocals distinctive and not unpleasant.
But really, it’s not about Meat Loaf. It’s about Steinman. Meat Loaf’s albums without Steinman as writer and producer were mostly commercial failures, unlike the other top artists you listed in the OP, who had more consistent success. I suspect that Steinman could have used Bonnie Tyler and done just as well.