Well, to be fair, with RBC you don't have to necessarily leave $5k or any amount in your account to get a fee waiver. The multi-product discount to which some of us have made reference can be obtained by holding two of CC, mortgage, or investment. There have been a number of discussions on RFD over the years about setting up a TFSA containing $0.01 and signing up for a no-fee Visa to get the fee rebate.
More broadly, the balance requirements for fee rebates have varied quite a lot amongst banks. As you noted, some require large-ish amounts like $5k, while others have been $3k or even $1k. When you get down to those lower balance requirements, the opportunity cost of keeping that money in a chequing account becomes pretty trivial. Most people seem to like to keep a couple grand in their chequing account anyway just for operational purposes to avoid LOC interest fees or worse, NSF fees (I guess there are probably a few that sequence a transfer from their savings to their chequing account every time they pay a bill, but IMO that would be a royal pain in the ass).