If you want to be picky, you need to get it right first. The actual term is frame. datagram is generally used to refer to layer 4 operation, and the term is not used anywhere in IEEE 802.3.

Also the GP is correct to say we fossilized on 1500 byte packets, since the layer 3 MTU is the relevant thing when talking about fossilization in the internet at large. This number was driven by 802.3's standard frame size being 1514 bytes, but that one is not even fossilized as much. It takes work, but you can control your own network and roll out jumbo frames. You can't roll out larger packets on the internet.