An interesting side effect of that is one can use the grid frequency to coordinate emergency power response - individual nodes (batteries, peaker plants, etc.) can react directly to the frequency measurement with generation or load, thus stabilizing the grid. Too much energy is equally an issue. Usually it's called fast frequency response these days.
Good point... oversupply lightens the load on the generator meaning not as much angular momentum is converted to magnetic flux then to an electric field. Unopposed the torque is able to increase the rotor's speed which directly determines grid frequency.
My grid tie solar system does exactly what you say. It monitors the frequency of grid power and matches it dynamically. There are defined parameters for how out of spec it can get and for how long. I don't recall the exact numbers but imagine 0.2Hz for 100ms, 0.5Hz for 1ms, 1Hz for 500ns. Same thing for voltage though that allows a much wider range.
In CA all grid tie solar also requires communication with the utility (through the manufacturer) with a backup connection source (Internet and LTE in my case). This is so if the grid is nearing capacity or going unstable the utility can command the inverters to allow a wider band of voltage and frequency. The last thing the grid needs in an unstable scenario is everyone's solar panels tripping off at the same time.
Technically the utility can also command the panels to stop production if there is an excess supply but they are limited in how long and how often they can do that.
Fun fact: The interconnect operators used to keep track of the average frequency over time and would run the grid slightly fast or slow to ensure the grid averaged 60Hz over time. This allowed clocks and such to maintain time by relying on the grid. That is no longer the case though. I think they still roughly aim for a 60Hz average but if they're behind by 0.01Hz over the past week they no longer run the grid at 60.05Hz for a while to "catch up".
Fun fact number 2 I just learned recently: Southern California used to be on 50Hz! That's right, the USA had split cycle just like Japan. Most of the country on 60Hz, SoCal on 50Hz. Right after WW2 they made the switch apparently. I guess a lot of stuff was dual frequency capable at the time but the utility provided assistance where required.
Fun fact number 3: Ever wonder why we have 110/220 or 115/230 or 120/240? Because every local utility picked their own standard: 110 (from Edison's DC system carried over into AC world), 115, or 120. It was not until relatively recently that we really standardized on 120/240 (+/- 5% which is 114 - 126 but with brief excursions allowed). That's why some old appliances might say 110 or 115 on them.
Fun fact number 4: 120/240 is a backwards compatibility hack. It was too late to change to 240 and 120 is (for physical reasons) better for electric lighting applications (thicker less fragile filament for same light output). How to solve this? Change your MV-LV transformers to 240 but center tap them. Instead of Line-Neutral you provide customers Line 1 - Neutral - Line 2. Connections across L1/L2 give you 240 volts, connections across L1-N or L2-N give you 120 volts! Everyone's happy! There is a NEMA plug standard for low-amp 240V. It has both blades horizontal (looks like the unimpressed smiley face). I wish it were more popular in kitchens for boiling water and such.
