One exception is GOOG / GOOGL which both trade actively, and there's not much difference in price.
The mechanism for a price divergence could be accumulation of the 10x shares to seize control, but even if you could buy the entire float, it wouldn't be enough to take control, so that mechanism never happens.
By voting rights, they have 10x (founder stock), 1x (trading as GOOGL), and 0x (trading as GOOG). The class with 10x voting rights does not trade publicly. The class with 1x voting rights does not have enough voting power to control the direction of the company so there is no real difference in perceived value between GOOG and GOOGL.
Employee stock awards are IIRC all in restricted shares of GOOG (0x voting rights) so they don't dilute the power of the founders.
Interestingly, the 10x shares held by Brin and Page constitute only 11% of the economic value of Alphabet, but 51% of the voting control.
And the 10x shares automatically convert to 1x shares upon transfer or inheritance, so if the founders cash out or die, the 10x supervoting power disappears.