> Typically, I will fall out with someone senior, like my line manager. It's normally over something mundane but definitely technical.
This is the most telling part. If it's mundane, I don't think it matters (for them) that the issue was technical. As mentioned in another comment, this likely leads to a loss of trust or respect. This can be both ways not just on one side.
There's a few ways to handle this: 1. accept the pattern and move on, 2. find ways to communicate better to reach some sort of agreement or compromise, 3. learn to "disagree and commit". One thing to realize is that as you report to your manager, they ultimately have the final say regardless of how technically 'wrong' it could be.
I too have had critical disagreements with senior technical or management. In some cases, I could let it go and work for a year or more before leaving out of boredom. Other times, if disagreements or lack of understanding recur, I may be on my way sooner. I've never regretted leaving and finding new opportunities. One thing that's worth trying is different sizes of companies and different stages of growth. Finding good large companies may be more rare as they're typically more conservative and move more slowly.
I didn't answer the question though. Is it just you? Maybe yes or only partly. But it also doesn't matter. It's also great that you can be so involved after 3-5 years, but realize that this is a double-edged sword. At the end of the day, it's a job that pays the bills for most people at the company. Take pride in your work but maybe not get too possessive about it, learn to let go like a child growing up and grow other parts of the system, there's always more. One thing that helps with the too much single-handed development is pair programming, alternating typing and navigating roles. If that doesn't work out, that's fine too--stick with what works.