It all depends on your definition of 'good'. SIBM, SCMHRD, or even IIM-A are not good universities for someone who has excelled throughout their academic career and wishes to attend Ivy League colleges.
SIBM and SCMHRD are absolutely good universities for someone who has been above average academically and wishes to study in India's top 20 B-School. In addition, aspects like curriculum, faculty member quality, infrastructure, and so on.
Every year, approximately 80-85k candidates apply for SNAP, of whom 2500-3000 are shortlisted for the GD-PI procedure, of which 400-500 are selected to study at these two colleges. If it answers your question about SIBM/SCMHRD being good colleges, I believe that is the ratio for many of India's top B-Schools.
In terms of ranking, SIBM is consistently ranked among the top 15 B-Schools in India; the rank ranges from 7 to 15, depending on the methodology and factors used. SCMHRD appears alongside, a few positions lower/higher for the same reasons stated above.
And people do consider Symbiosis a great brand, provided they're from the industry or closely follow education around business administration. They are well aware of the outstanding work of our alumni. Other persons who are not interested in business news or MBA as a discipline may be unaware of B-Schools other than IIMs and XLRI.
And, certainly, brand dilution occurs when the number of universities with the same name increases, especially when admission is very easy. The same is true for NITs, IITs, and IIMs. While IIM-A is a fantastic brand, IIM Kashipur, while being an IIM, is not. SIBM Pune is a more powerful brand than Symbiosis.