https://www.space.com/james-webb-space-telescope-fueling-for-launch
The thing that's going to make hubble look like dog shit if it doesn't explode first.
Webb
adds to the capabilities of NASA's Great Observatories (of the original four, Hubble and Chandra still operating), but does not replace the capabilities of Hubble. Webb only operates as low as 0.6 um wavelength, so will not be able to take "natural color" images (as the human eye would see it) of planets, nebulae, galaxies, etc., nor investigate any phenomena in the UV. Webb's advantage is extending the distance (and hence the ability to view back further in time) by having a larger mirror that can collect dimmer light, and having a wavelength capability farther out in the IR to see objects that have been red-shifted more (because they're farther away and hence travelling faster away from us, and emit farther out in the IR).
Added capability, not better quality replacement capability.