What I'm trying to make happen:

Upload a Realm World download from a friend to my Realm. 

I. At first when I successfully imported the World Download, checked by playing locally to see if the file was broken, etc. Nothing was wrong with the file/import process. 

II. Attempt to click on "Play on Realm" created a 10 player Realm, the process completes and I get loaded to a completely new seeded world. 

III. Attempt to rectify by clicking "Replace Realm" from the edit Realm/World page. Several failed attempts with varying errors depending on the whim of rngesus?

Several attempts have led to the process "completing" and the "All done" dialogue box with a "Let's Go" button appears. 

Noting the "file" size is differs between the "Choose Realm" (196.7MB) page and the "All done" (195.5MB) page. Clicking the "Let's Go" button in this case connects me to the same "new" world created in step II.

IV. Have attempted the "Replace World" method several times to the same result. Decided to bite the bullet for science and attempted to "Play on Realm" again, subscribing to another realm. Again this just leads to another new seeded world. All these new worlds aren't even a reset version of the world I'm trying to upload. Just straight out a different fresh new world.