It takes a long time for dust to settle in Vintage.
That said, I don't think any amount of "shake up" is inherently bad. When Wizards prints interactive cards that create new decks, that's great for the format. When Wizards prints dominant cards that entrench established archetypes and are un-interactive, that's bad for the format. Both can be considered a "shake up". Right now, I feel like Karn and Narset are analagous to reprinting Lodestone Golem (or whatever broken, restricted colorless card) and Dig Through Time, in terms of a shake up. In the same set. Which can be pretty miserable to play.
Modern Horizons looks much more positive in that the spoiled cards, don't inherently slot into the Karn - Narset decks (though 8-Force Dredge isn't something I look forward to). But most are going to be role players and not really format defining cards. I still think the format will be defined by Karn - Narset - Bazaar.