Here are some notes that might be helpful to anyone coming across this (or you, if you don’t want to be limited by who can see your activities).
Where are my older Garmin activities? describes how to get around the issue of Garmin’s 5 year limitation.
How to connect multiple tracking services to a single CityStrides account covers the process of adding multiple tracking services.
It sounds like you did this correctly, but had already logged into CityStrides via Strava at some point beforehand - so instead of connecting the accounts, it logged you into the second one. 
I’ll try and find some time to improve that situation.
Your revoke/re-connect process works, but potentially results in tons of data being deleted and recreated. I have the ability to merge accounts, which is much more efficient, so if you’re reading along & need that help, please ask.