The audition is what counts for a MM acceptance. There are many paths to achieve the voice needed to succeed in those auditions. Foremost is a teacher that can develop a young singer. Performance opportunities while great are not the biggest factor. DD had no roles as an UG, had a fabulous teacher and when she went to grad school had major roles for both years. As an undergrad there can be other opportunities in recitals and scenes programs.
While you can no longer judge by those who are even just 10 years out of grad school, DD’s friends who are little older than her and are having some success in YAPs and in small roles had many different undergrad experiences, but all had fabulous grad experiences. They all had great undergrad teachers, for them. Students who were in the MM program at Rice did not all come from conservatories. One who was in her studio came from a smaller regional university. She won the MONC competition and is working, including at the MET, now. Those without the BM grounding had to stay an extra year to catch up on course work they had not covered as an undergrad, something to consider.
If you do not do a BM, then the things that you have to learn need to be covered somehow. Lessons, performances, music theory, language, sight singing, etc. Stepping into a MM cold will not happen. As @colorsturakid mentions, there is more to this profession than juist singing but there are many paths to achieving it. Many will say a well rounded education is just as important for a singer since that gives a good grounding in more life experiences from which to draw in performances. DD found the combination of an excellent university and excellent music school with a great teacher fit the bill for her. She is just starting into the YAP audition world so we will see how successfull it all has been, in about 5 years.