Default Semantic Model editing via the web browser is HORRIBLE, needs to be better

I went to edit the (Default) Semantic Model attached to a Warehouse. WHY is this not available if I click on the Semantic Model itself? That seem to be the logical place to make this available to the users.

Then when I went to start editing, I added a page by clicking the [+] at the bottom. No page showed up. So I tried a second and third and multiple times. It told me there was an error and that it was refreshing. I ended up with 7 extra tabs at the bottom because the browser could not refresh.

I click the [x] to delete a tab, but it's still there. Clicking the Refresh button at the top does nothing.

In the end, I have to open a new browser tab and navigate to the Warehouse and Model Layouts to see changes.

Also, resizing the divider between the Explorer and the Model Layout is buggy, like I simply want to drag the slider over a bit, but it latches onto my mouse even after I release the mouse button.

In short, the user interface experience is horrible and need a lot of help.