Even if that were true, how could you possibly know it?

Observing animals' behavior (in the wild and through experiments like the one here) and studying how their brains work to see that they often have the same kind of mental features as us (including whichever you'd classify as consciousness) - just at varying degrees of sophistication.

Some would argue that "consciousness" is something non-physical that has no impact on the physical world, and so is not physically detectable or responsible for any behavior, but I feel then it inherently cannot be whatever we mean by "consciousness" that we're directly aware of and talking about in the physical world (because that itself is a physical impact).

... with insects on the low side, humans are mid, and dogs are top

Dogs are on top but just below cats haha

Maybe it is the same level of consciousness but different physical limitations? Simply imagine being locked in in an insect body with different perception and abilities, and a wiped memory.

Then maybe orcas are much more conscious than us?