Not having existing CVN leading to delay yes. But relatively speaking, no, if you put it in context.
002: first ever domestic build carrier. Many basic stuff had to be designed, tested, even the basic building process is new.
003: The first catapult carrier, for one. The first carrier design not based on Varyag blueprints. In some ways this is a bigger leap than 002.
Relative to these milestone and cause for delay, a new propulsion change for 004 is lesser concern than those. So a significantly faster construction is expected, 2028 or not. If any complication, it might be the fitting out phase, not the parts prior to launch.