Yes, but I think there are different sets of users.
Users like you probably are going to want to be where the largest and most diverse group of people is, which will be the largest service. That is currently, by far and away, Twitter. Moving those people away from Twitter, if they do not already have a strong motivation (either socio-political, or use policy, or because their friends and follows have all moved somewhere else), is unlikely, but in any case most of the users who are like you are going to be with the largest service. I doubt that we will have two equally sized services, at least not for quite some time, because many people who are not very disaffected with Twitter will not move.
The most disaffected groups are the ones who have the highest incentive to move to a new platform, and currently many of these fall into the "disgruntled" category, often for socio-political reasons. It makes sense to think that these will be over-represented in the group that makes a serious effort to move to the new platform (if you look at who comprised the surge of users of Mastodon, or something like Post, you can see that this is definitely the case). Bluesky will, at least initially, be like this, I think. In the long run, though, you're right -- most people will want to be with the larger, diverse platform.
Nostr will be more like Mastodon was before Elon ... a smallish place for enthusiasts of decentralization, albeit following a different protocol than Mastodon, of course.
Bluesky is already the new Twitter, you can tell. The cool kids all want to be on Bluesky. In effect, the very low rate drip of invites approach they are following, coupled with a virtual megaton of almost entirely gushing, breathless positive stories from the tech press are generating a high pent-up demand and a sense of virality even while it has a tiny userbase. The people running it are very clever, and are clearly doing everything they can to become the alternative for disgruntled Twitter users that Mastodon, Nostr and others are not (and arguably never were trying to be ... Bluesky is, by contrast, trying like heck to be exactly that).
Does this mean Twitter dies? No, I don't think so. What I think it means, though, is that, like the MSM, we will have likely two microblogging platforms that are broken into socio-ideological camps, like we have with most of the other media. It's new for social media, of course (not that there haven't been wing platforms before, but they have been small), but not new for media in general or the internet in general. And one could say that it's actually somewhat surprising that it took so long for this kind of split to happen in social media as well, but it kind of "feels right" that it's happening, given the very divergent ways that people have reacted to Twitter over the past year. It seems "right" that there should be separate services for people based on the kind of ideology and views they prefer, since this is how pretty much everyone rolls in every other aspect of the media already anyway.
This is the issue from the consumer point of view. For most people, it's too expensive to subscribe to more than a few (like less than 5) writers on Substack, and that excludes the newsletters that have the really high-expertised content (which tend to be quite expensive on a standalone basis, as one would expect). This makes sense for the writers, but as a consumer, it's very limited. I personally only read a few Substacks because I don't want to spend the money to subscribe to more than a few of them, given other subscription costs already being incurred elsewhere. No doubt many other potential readers are in a similar position.
It will be interesting to see how things shake out, certainly, and where we are in the microblogging space in, say, 6 months.