It comes down to valve time-area. When you spin a motor faster you have less time to move a given mass charge into the combustion chamber. Yes, they would but you are assuming they are heavier. I don't know the relative mass differences but there are things engine builders do to mitigate that tendency; things such as race springs and lighter rocker arms. The inlet ports on an RH7 are reported as 32mm which are as big as they got from the factory for all heads. So your last statement is conjecture and goes nowhere. Furthermore, one really cannot draw conclusions from isolated aspects of an engine build.