I do know how it works, as I have a PS4 and have had PS+ for a bit now. However, before I had PS+, I could still play some games with limited online functionality. In Driveclub for example, I could still make a club, get other people in my club, compete in time trials, and have my times appear on the leaderboards, when I didn't have a PS+ subscription. In The Crew, I could join online free roam sessions without PS+. I couldn't join races with other people in either game, but I still had some limited online functionality.
All I said was I wouldn't rule out GTS having a small amount of online function without PS+. You definitely won't be able to race against others online without it, but you may be able to have your time trial times appear on leaderboards. Like I said, DC allowed it, and that was a PS4 exclusive.