I too avoided syncing with Google contacts for a long time.... many many years in fact.
I only had the contacts list on my phone itself, and I was good about doing backups.
In fact, I had an app backing it up and sending it to my personal email account and stored there in a folder. Also backed it up to my PC 'once in a blue moon'....
I thought everything was "working just fine", but my backup periods were too far apart for the realities of life.
and one day, I decided to get a new phone. Something went bonkers with that phone and I just decided on a whim that it would be easier to just FDR the phone and import all of my backups and get on with life.
Well, it just so happened, that I had attended a conference acquiring a lot of new info in between the last backup, and when I restarted that phone from scratch.... Life didn't end right there, but it caused me a lot of discontent.... I still have the previous phone, I kept it for a spare/backup. Checked the contacts list on it, and it was woefully out of date....
That was when I decided that keeping contacts on the phone internally was a very, very bad idea.
since that moment in time, all of my new contacts are now sync'd with Google Contacts and calendar. Life is much smoother now.