But the OP refers to more than just civ switching and ages. The unhappiness of the playerbase in the aggregate isn't confined to one or two changes. Everything should be taken into account. About the only things that aren't controversial are a few peripheral changes like commanders and navigable rivers.
There isn't a clear line demarcating whether something is a 2.0 version of the previous iteration, but if you take away the changes made in Civ7 one by one, it will eventually become Civ 6 2.0. And the bigger the changes that you take away, the more movement the needle makes towards that mark. In any case, it isn't necessary to define an ontological point where it would become 2.0. All you need is the perception in the market that it's just Civ 6 2.0, and as the producer, you could only guess as to what that point is when you set off to make the game.
Again, the OP isn't focusing on a single issue or even a single group's perspective. It's not about being positive or negative or taking a stance towards player reception - something people keep failing to understand. It's taking a step back from the personal to analyse the big picture using concepts such as the product/franchise lifecycle. And the assumptions that it makes shouldn't be controversial, to wit:
- People tend to be resistant towards change (for something they're familiar with).
- Nothing in the market lasts forever (and everything will eventually be replaced by something else).
To restate the main thesis of the OP differently, the more popular a product or franchise is, the larger the commercial risk that Assumption 1 poses. Conversely, the less open producers are to innovating and making changes to a product or franchise, the more likely Assumption 2 will catch up to them.
And the corollary to that is the pushback that Civ7 is receiving represents a realisation of this phenomenon.