Nobody can promise a specific ranking outcome, and anyone who does is guessing. What can be controlled is the technical execution, and that is where migrations usually go wrong.
Before anything moves, we crawl the existing site and record every URL, canonical tag and metadata value as a baseline. The redirect map is built from that crawl, not from pattern guesses, and one rule is enforced: no chains. A goes straight to C. After launch we re-crawl, compare against the baseline, and keep watching coverage and indexing until they settle.