Quite correct, Bill; in Ontario, for example, entire hydraulic generating stations are routinely used as the frequency control "swing units." Plus, since the entire Eastern Interconnection is rather huge, frequency control includes the adjustment of phase shifters along with generating units [and possibly, in the future, an asynchrounous tie across Lake Erie] to maintain the loadings of the tie lines to other entities as scheduled, et cetera and so forth.
Given the foregoing, unit governors on what is, if not an "infinite bus," a finitely huge one, respond only very minutely to the more-or-less continuous changes to Interconnection frequency, and will only make gross changes in response to major system disturbances...and, generally speaking, anything less than that, commonly described as a "limited system contingency," won't cause much wiggle at all on the vast majority of the governors on said interconnected units.
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]