That episode was set thousands and thousands of years in the future, ipso facto the Cyberrace had been upgrading for thousands and thousands of years.
You can say that the Cybermen originally achieved perfection and decided that that was it.
However, there have been so many wardrobe redesigns over the years.
That it's possible to deduce that each of those wardrobe redesigns were a massive and fundamental upgrade.
Upgrades used to probably have to come from the cybercontroller level and only then effect the next generation of Cybermen being produced from the factories.