I'm an engineer working for a startup entering a period of high-growth. One year ago, I was the first (non-executive) full-time engineer. Currently I'm one of six, and in a year's time I'll likely be one of 20. As we continue to add engineers and engineering managers, I'm not quite sure how to find my new place within the organization. How have you adapted to your team growing around and above you without feeling like you're being replaced?
What happened to me is that I went from being _the_ key employee who built and architected major parts of everything, to slowly but steadily being stripped of every single task, meeting, project, in favor of new people who were brought in to cover those areas they had experience with on their resume (but not necessarily performed at a higher level even after their ramp-up period, in my obviously biased opinion).
In the end (after about a couple years from my productivity peak) I ended up as a completely disposable resource, with literally nobody paying attention to anything I had to say. It surely was a very tough mental exercise for me, I had to brain dump all I knew about the technology to all these new hires dozens of times, knowing that they would completely replace me in months and leave me task-less, which they did. I had crazy impostor syndrome constantly thinking "do I suck this much that they are replacing me for everything?" (the answer was no: I was able to obtain job offers from 4 FAANG companies, and I joined one).
The worst part of all is that nobody will tell you what's going to happen, your manager (manager that you didn't have when you joined since you built the damn thing when nobody was even around!) and everyone around you will keep praising you. But each and every single day, one little piece of the puzzle will be taken away from you and given to the new hire with the shiny experience on the resume.
What "saved" my mental sanity is that I am a good negotiator and so I was able to negotiate a decent equity package at the beginning and put it in writing in my contract (2%+). Unless the company is doing particularly bad business-wise, screwing up common shareholders, especially if you early exercise, it's not that easy, so throughout all this period I took comfort in the fact that I was still likely vesting more shares than anyone else non-exec who was brought in to replace me.
I have left that company now, but so far it paid off, since I've already been able to obtain some liquidity for those shares by selling some of them to private parties. In the vast majority of cases, it would have been worthless as startup equity ends up underwater.
https://blog.codinghorror.com/commandos-infantry-and-police/
It might be the case that you excel at the "first wave", but are not interested or not talented at the kind of work that needs to be done at a later stage of the company lifecycle. If so, that's nothing to be ashamed of.
edit: i guess what i am arguing is that it isn't a failure if your skills are better suited to one early phase of a business lifecycle. these skills are highly valuable in the right context. if that's the case, it could be win-win-win outcome (for you, your current employer, and your next employer) for you to switch to a different company that is in the phase you are most effective at, if your current employer has sucessfully grown out of that phase.
If you were not needed, you would have been let go already. Just do your work as you are used to from the beginning, keep learning new things and be as flexible as a gymnast when it comes to learning. THat will make you more valuable.
Unlike a big company where there's a very strict hierarchy and structure, and all you have to do to rise up in the ranks is put in the time, in a startup it's a free-for-all.
That means you have the power to change your situation. As more engineers join and take on pieces of work you've been involved in, you can start to scale yourself. Be a leader, start new initiatives, think about the bigger picture instead of just your job, and inspire others to see your vision.
You don't need a fancy exec title to be a leader. You don't need permission. You just need to start behaving like one.
I think the first step would be making sure you know what you want, they know what you want, and everyone is on the same page to get there.
I mean, are you okay just being another engineer or do you want to a key technical leader as the organization grows? Those can be two very different roles.