The technical difference is that E-meet use Web-RTC as streaming method. E-summit just embed a stream, the stream can be from any provider of your choice.
The longer version:
E-meet is a complete video conferencing solution. You can broadcast people in real time without delay. This means that you can have a studio and participants talking with each other without delay. You can also create workshops and divide the audience inte groups with up to 16 simultaneous speakers. There are also possibility to broadcast you studio via virtual cam.
For E-summit you have two different ways to work with embeded streams. Either put the video in project settings this will create an injected video in the header. This is very handy if you want to show the stream always. You can also build a video stream block and put it whereever you want in the timeline. This is perfect if you want to build a custom layout or maybe have more than one stream at the time.
The stream block can also be combined into an E-meet.