Eris is essentially the same size as Pluto and has a larger mass.
Why remove Pluto?
The definition of a Planet could be whatever we want. It could be "these named entities are planets, other things are not planets" if we wanted. That makes a hell of a lot more sense to me than anything else, because eventually we are going to find planets which really blur the boundaries we have currently. Until we observe the entire universe, any set of rules we come up with are going to appear to be wrong in some situations.
Mercury, Venus, Earth, Mars, Ceres, Pallas, Juno, Vesta, Jupiter, Saturn, Uranus, Neptune, Pluto, Eris, Makemake
(Plus some more).
Why should giant planets be in same category as normal ones? Why mixing ringed with non-ringed? Why mixing moonless with moon-enabled? Gas/liquid ones and solids? I could go on for a long time.
Current estimates expect about 200 Pluto-sized objects in the Kuiper belt and about 10'000 in the surrounding region.
Compared with 4 rocky planets, 2 gas giants and 2 ice giants.