Boston Consulting Group Software Engineer Data Visualization Manager interview questions

Worst experience and one will not expect such process from a leading company. The entire interview process dragged for more than 4 months. Interview consisted of HR phone screening, 1 written test, 5 rounds of zoom call. I am 100% sure based on my 13 years work experience in BI and Analytics that people who interviewed me were not experts in BI, Analytics, Data warehouse or Data visualization. However they rejected on the base of technical knowledge, not sure what else could be the answers to the questions they asked. I really doubt how people have reached to this stage where they interview for such a company who is pioneer in consulting and decades old. One of the interviewer asked my compensation in between the interview discussion which i had already communicated before to HR during my phone screening. I appreciate the co-ordination and feedback on next steps given by HR throughout the interview process.