I agree with him. People tend to sit on old models without noticing the change.
X may herald categorising and partitioning users into niches. That actually means each person belongs to a certain community and will be shown to that community community limiting your reach.
To break your reach out of that exclusive community, you have to create content that stretches into other communities and appeals to wider communities.
Hence, you have to be versatile if the algorithm has to show you to more people outside your niche.