Yup. Even though in Firefox Android 'regular' that's at the same page, as you noted it's not always that fast, especially for low end phones. But with this new Firefox Preview even the Plus button is not at the same 'position', and the new page opening up with animation takes even more time.
See my other comment, the "+" button is useless is Firefox Preview, there's not a single use case where you need it. It was probably added for people who didn't notice that the address/search bar is already here, or with "muscle memory" of searching for a "+"
At the time you opened the tab menu, you're already in a new tab.
Horizontal space is somewhat of a premium though, especially if things like reader mode or buttons provided by addons as available in the current Firefox will return to the URL bar once more.
And the current design for Fenix doesn't help in that regard by having quite a bit more white space - the tab counter and menu button take up approx. 50 % more width than they do in the current Firefox.
