There is a bit of a difference. "See you soon" may be written as just a factual statement. it's a statement that "I will see you soon." "I hope to see you soon" expresses that they will not just see you but that they're looking forward to seeing you. It also might express doubt about seeing you soon. With "I hope" it means the person doesn't know whether they will see you soon.

See you soon is short for , I will see you soon. So you can now see the small , usually insignificant difference. I hope to see you soon, and I will see you soon. So if you most likely will see someone again, you can say "See you soon" , If it is uncertain if you will see the person again soon, then say" I hope to see you soon."

Do you mean semantic tone or acoustic tone?