yeah id think Dio or Bruce D would be closer to an Opera style than Rob. They both had more of a “chest voice” carried up pretty high whereas Rob just usually went with more of a screamy rock sound for his high stuff.
Gotta remember that for opera guys a “high C” is the money note. A high C is a C5. Well for rock and roll a C5 aint that high. The difference being an opera guy hits a C5 with a thicker and darker tone which is WAY harder and takes about 10 years of training lol. A rock guy wont hit that note like that, rather he will gradually thin out into head voice as he goes higher.
Between Bruce and Rob (and Dio), Bruce was a bit closer to that heavy chesty high voice whereas Rob was a bit more in the classic rock head voice vibe.