In many instances Rhino 5’s version of the “Blend surface” performed better than that of Rhino 6 and Rhino 7. Sometimes, the “Interior shapes” option introduced by Rhino 6 adds a massive amount of additional control points with no obvious reason (including on very simple input geometry), whereas Rhino 5’s “Blend surface” could achieve the same results with cleaner surface consisting far less control points. To do the same, Rhino 6’ and Rhino 7’s “Blend surface” have to add those extra control points, otherwise it may lose continuity if the “Interior shapes” is turned off.
Also, the handles of the additional interior shapes can’t be controlled in a user-friendly way manually IF the major end handles at either side of the blend surface were modified with the mouse.
Another disadvantage of “Blend surface” is that there is no separate control with dedicated sliders for the opposite handles. For example, the sliders can’t move only one of the handles with number 1 and one of the sliders with number 2. Instead, each of the two sliders controls the entire surface edge simultaneously (both handles from side 1 or both handles from side 2) which is useful sometimes, but may be unwanted in many situations.
If you check my older port at the beginning of this topic I proposed use of 4 sliders instead of 2, with tick boxes allowing to lock 2, 3 or all 4 of them together. So, instead of handle 1 and handle 2, it should have handle 1a, handle 1b, handle 2a and handle 2b. This gives the user a total control over the shape of the blend surface that’s also adjustable with a slider and a numerical input. The “VSR” plug-in for Rhino 5 allowed that function and it was extremely useful.