Cultivation progressed differently for different beings. The cultivation levels, as humans identified them, were a good standard to measure strength by, but other races may skip over certain realms. A very simple example of this was the fact that countless races were born at a higher cultivation level, such as dragons.
So while an upgrade for a human may result in extensive growth in power, such as moving from the Nascent realm to the Earth Immortal realm, that did not mean much on a universal scale. That was just the level of growth a human body and soul could sustain, before they needed to strengthen or amend their being, making it more amenable to more growth.
So, for a World Seed Lotus, growth looked like transforming from a lotus into a world. The power difference between those levels was absolutely massive.