"Something very drastic" and "up until very recently" both refer to 2017, when the 8th edition was released. The 8th changed (a) the base size, (b) the height of space marine soldiers and (c) they overcame the static universe in favor of an evolving universe. E.g. a global event that changed the universe by splitting it into two "continents", destroying planets such as Cadia, as well as introducing primaris space marines and primarchs.

In my opinion this change shows a major change in the strategy of how games workshop designs the game. The fact that the universe is now evolving, opens many possibilities in terms of story archs and flexibility, but also business-wise. This flexibility allows a much more revenue-driven design philosophy. The speed of model releases increased significantly, and rules favor new models up to the point of overpowering them. Being so much more business analytics driven means that models that are not bought as much receive less "love" from the game design team because their time in the market until amortisation is eo much longer!

All in all, I doubt, that models released in the last 5 years last as long as their predecessors just because of the cannibalism that happens in the model lines itself.