It's true that normally when using http websites the exit node you use can theoretically look at whatever you are sending, and yes using a https proxy would prevent that from happening, however that https proxy would be able to snoop on your data in the exact same way that the exit node would so you are basically just shifting your trust from the exit node to the proxy, so using a https proxy doesn't really fix the problem.

Just out of curiosity, in this use scenario, do the connections work like

  user <==> proxy <==> Entry node <==> Relay node <==> Exit node <---> destination 

or

 user <==> Entry node <==> Relay node <==> Exit node <==> proxy <---> destination 

False.

Say you visit example.com this way. Unless example.com supports https, that last connection is still going to be unencrypted. The only difference is that last connection would be between the proxy site and example.com instead of an exit node and example.com. There might be some reasons to trust a proxy site more than a random exit node. But on the other hand, the exit node isn't totally out of the picture, it could still try a MitM attack using a fake certificate for the proxy site, so in some sense you now have two potential eavesdroppers instead of just one.