In my experience working with and leading software engineers, I have seen mid-level Engineers produce outcomes worthy of a Senior, and seniors who are only so in title. High-performing mid-levels eventually overtook under-performing seniors. How you become a Senior Software Engineer is important.
If you become a Senior because you’re the last man standing or the one with the longest tenure. I am afraid that future upward movement may be challenging. Especially, if you decide to go elsewhere. I have been fortunate to directly mentor a couple of engineers to become Senior, and witness the journey of others.