Amount of mining depends on amount of transaction fees, not the other way around.
With no block subsidy, if the amount of txs drops 10x, then there will be 10x less rewards available for miners (actually even less if you go from (nearly) full blocks to never full blocks) and so mining must decrease 10x to remain profitable.
Sorry but you've still got this all wrong.
Sorry, but your long rambling utterly failed to show anything wrong in either statement.
Your only argument is that if we assume number of txs to be fixed, then by definition nothing depends on it. Duh.