If you go the blend route, another thing you can do is adjust the bulge factor, if you reduce it the blend will become more flattened and get close to your original shape, here is an example where I typed in a bulge factor of 0.5 for each of the 4 blends:



The central surface is still not completely flat like in your original, but it is getting pretty close to it, it is less bendy than the previous one. And then it still has the property that it is smooth with the other pieces where they touch, which makes the fillet work.

Let me know if you would like a more step-by-step run-through for how this one was constructed.

- Michael