I see where you're coming from, I used to hold the same perspective. But there were already a couple of "unrealistic" plot elements before that - like the gravitational anomalies in their house, or the conveniently-placed-and-magically-kept-open-and-large-enough wormhole, which doesn't seem much less Deus ex machina than the tesseract at the end.

Maybe the biggest difference in perspective is in the "power of love" - I don't think the plot is using that as a solution, that's just Coopers interpretation. The solution is the tesseract created by the future humans, which isn't that much more unrealistic than the wormhole. It was a unique and visually incredibly interesting interpretation of the supposed singularity at the center of a black hole, and sadly there's probably no way we could ever even form theories on what that might look like.

In the end, I'm not sure there's anything less unrealistic that could finish the plot, and I'm fine with the sci-fi elements. But that doesn't make your view any less valid!