A333 fuselage daimeter 5.64m, B777 6.19m, B747 6.49m.
Boeing 767 is 503 cm, "Boeing" MD-11 and DC-10 are 602 cm... for completeness, Tristar is 597 cm and Il-86 and -96 are 608 cm.
It's more comparable to a 767 than a 747 or 777, certainly in terms of size.
Looking above, 330 is 61 cm wider than 767 and 55 cm narrower than 777. So, more comparable to 777.
As I have written before the seating (manufacturer of seats, width, pitch, etc), and "comfort" thereof, is entirely down to how the airline has chosen to fit out the cabin. The airframe manufacturers just do the basic shell.
The seat manufacturer and pitch are up to airline. Width - not so much so. The basic shell gives the total width, and sidewall shape. The airline can then choose the number of seats abreast - which has to be integer. That gives the seat width.
which are virtually identical in every aspect, except for the A340-500 and A340-600 which are of course longer in length.
And 330-300 is longer than 330-200. A300 and A310 are shorter, but also have the same cabin width.
One notable difference is the sidewall shape. 777 (and 747 maindeck) has more vertical sidewall, compared to A300 whose sidewall slopes more inward in upper parts.
But this difference of course only matters for window seats - and while some 777-s have 2-5-2 seating with therefore more comfortable window seats than on A300, Boeing pushes 3-3-3 seating, making window seats double excuse seats. Allegedly because Boeing has never invented an IFE box for 4 seats.