I expect growth of a crypto exchange is a lot easier when you can steal client deposits to fuel additional growth.

You have it backwards. The deposits were used to fuel a separate trading business. All exchanges use customer deposits to grow their business.

No. That is incorrect. A brokerage / exchange may not use customer assets for their own benefit. They are not a bank -- they are custodians. If they are doing that, they are committing a crime.

https://www.law.cornell.edu/cfr/text/17/240.15c3-3

I believe Binance was bigger than FTX. That being said, it’s hard to tell how big any of these organizations really are because they do not release audited financial statements.