Objectively speaking, changelings are biologically superior to every other species. Everything any other creature can achieve, a changeling can replicate, but a changeling itself is not limited to a single form or set of forms in the way any other creature is.

This fact alone is enough to prove how a changeling is preferable to any other creature. However, it is not all. Not only are changelings able to replicate anything other species can do, their own species is in itself better than any other.

Changelings in their natural form posses both flight and magic, already putting them on par with alicorns in terms of versatility. What's more, Chrysalis and her soldiers have on more than one occasion defeated alicorns, proving they are in fact not simply equal but superior to them.

Chrysalis defeating Celestia in duel proves the strongest changeling has magic greater than the strongest pony. But if that wasn't enough, changelings have been shown to be able to enhance themselves. Both Pharynx and Ocellus have displayed transformations far more physically strong than their normal shape, providing changelings are not constrained by the abilities of the form they normally exist in.

On top of all this, changelings can grow even more powerful simply by feeding on love. And in their current, perfected state, they themselves produce love, meaning they can constantly immerse themselves in the collective share of emotion and become stronger and stronger through it.

This all leads to one simple conclusion: not only can changelings do anything any other species can, they can do it better, and they can do more. Once factoring all of this, plus the superior insect-like ability to communicate to one another, plus the availability of materials that disable all types of magic but their own, it becomes undeniable that changelings are superior as a species to anything else.

You may now ask yourself why changelings failed to conquer Equestria if they were the superior. It is down to two factors, closely related: Chrysalis's shortcomings as a leader, and the imperfect state the species previously existed in, which forced them into a parasitic, predatory lifestyle.

Both of these have now been dealt with. Changelings are now in their perfected state, and under the guide of a far wiser leader. Of course, though, they are still vastly unnumbered by the combined ranks of the other species, so a direct attempt at seizing control over them would be suicidal.

However, this is not an issue. There is instead a far more simple and safer way for changelings to obtain control, one that will secure their position as the supreme species for the rest of eternity, as they deserve: the Nonhostile Changeling Takeover.

I had some idea about the history of it as well:

Maybe, long ago, something similar was happening. And no creature was happy about that, so they basically alled for a huuge fight to basically exterminate or at least reduce Changeling numbers and push them out of their lands. Many died as a result and even more began to starve, resulting in the black holey changelings. (malnutrition etc.).

Over time this was forgotten and became legends, but the changelings survived. And Twilight, unknowingly what she would do, has led them back in.

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That could definitely be integrated into a story. I'm not sure if I would want to keep it for the canon I'm working with, but if anyone wants to write about that they are welcome to do so.

Wasn't Chrysalis only able to defeat Celestia in A Canterlot Wedding because of all the extra love she was able to absorb? Unless you're pointing out the fact that because of their ability to enhance themselves by absorbing love, the have no practical cap to their power level? Regardless, I seem to agree with every other point you make. Praise our changeling overlords!

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While that is true, it certainly sets a precedent on how changelings could replicate that. And Chrysalis just had the unwilling love of a single pony, with many more creatures to feed on they could grow even stronger. And they most likely can simply empower themselves with each other's love. And on top of that, the changelings later captured not only Celestia, but all the other princesses and the Mane 6 too. So they're clearly capable of overpowering even the strongest of ponies. I am glad you too agree that changelings are superior.

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You may now ask yourself why changelings failed to conquer Equestria if they were the superior. It is down to two factors, closely related: Chrysalis's shortcomings as a leader, and the imperfect state the species previously existed in, which forced them into a parasitic, predatory lifestyle.

How dare you question the glory of a true, authoritative leader!? Are your genes truly pure, or are you a filthy mutant?

(OOC though, fun canon idea)