I think there's a widespread wrongful impression about the size of the 055. When the PLAN launched the 055 project, they didn't issue displacement requirements, they issued combat capability requirements and 701st had to design a ship that could satisfy them. The specs given by the PLAN were so demanding that 701st anticipated a 20,000t design to fit the sheer number of systems required to satisfy those specs. This thankfully didn't happen thanks to masterful spatial optimisation and redundancy elimination by 701st Institute's engineers.
The 055's displacement is impressive not because it's large but precisely because it's not. A mere 10,000t normal displacement for a ship with the 055's capabilities is illustrative of the extreme competency possessed by the naval architects who designed it. Let's not forget the people who designed the 052C, itself an impressive class, initially thought they needed 20,000t of displacement to satisfy the 055's requirements. Ponder how ridiculously powerful a 20,000t combatant with the technology level of the 052C would've been and realise that such a ship actually exists but only displaces 10,000t and China is building six of them simultaneously. By halving the 055's displacement without reducing the capabilities, 701st allowed China to build and operate more of those ships without devoting more resources. It is this sort of efficient use of resources that led to the West's triumph over the USSR and it is also how China intends to eventually outcompete the incumbent hegemon.
What features of 055 would have required a 20000t ship? Genuinely curious, maybe the radar system requirement or the electric generation capabilities to support it?