Correct, as long as the instance your account is in federated with all other instances you're subscribed to, you don't have to switch accounts.

Now, defederation is another issue if you want to see the widest possible amount of content. What's going to happen is ideologically opposed instances are going to defederate each other, so left-wing instances are going to defederate right-wing ones and vice versa. So if you're a user who wants to see the content from both sides, you'll have to create multiple accounts in each "cluster" of federated instances. It's kind of annoying to be honest, it makes it hard to discover communities just because your instance admin decided to defederate from them and encourages echo chambers, but it it's the best we've got.