thanks for the PM. I am doing some analysis.
[1] One interesting fact: your competitor has
58% exact match for your primary keyword.
can you tell me what your number is. take a look at this url
https://www.semrush.com/analytics/backlinks/overview/YOURDOMAIN:root_domain
replace YOURDOMAIN with your own url
look at the bottom left panel and gives you that percentage
[2] also, when I use VPN and do search from different countries, i get a different result for the competitor that you mentioned. I think this is another culprit. Depending on IP of the majority of the backlinks, it impacts your search result. in the same URL i gave you above, check the country box and compare the top 3 countries to yours and see if there is a major difference.
[3] also, if you have friends from other countries, please ask them to search for your keyword and tell you what your competitor is ranking and also what you are ranking.
p.s. reason why i am writing this in public and not in PM, is that we call can better understand what google is up to.
p.s.s. your competitor sitting at 58% is probably the primary reason why they are ranking well above you. you could not be ranking at the top for 3 years, if you had 58% exact match anchors!