Supersized rocky planets are out there.

[Anomalocaris]

I believe the current consensus is all the gas giants in our solar sytem have solid cores of heavy elements. The core of Jupiter, if stripped bare of the overlying hydrogen and helium mantle, would be very similar in mass, but somewhat smaller in size and higher in density, compare to this newly discovered "mega"earth.

IIRC, the exact composition of Jupiter's core is subject to debate. It's core mass is suggestive of heavy elements - though I would not expect it to be "solid" due to pressure and heat. However, there appears to be some controversy about the presence of significant portions of heavy elements

The pressure would enhance the chance of it being solid if it is a distinct entity. The existence of singificant portion of heavy elements is deduced from the condition required for it to have attract its inventory of light elements during its formation. I think there is little doubt these heavy element formed a distinct core sometime during Jupiter's formation and early history. The gravity profile of the planet also suggests a matching dense entity continue to exist in the middle of jupiter. The question is whether the core later mixed with the lower mantle to form a rather blurry instinct central zone, or whether it remained a separate and distinct core with a sharp compositional transition.

But I think either way, it would be possible to strip Jupiter of most of its gaseous envelope and metalic hydrogen mantle and leave behind something like the mega-earth.