This is PCars 2's second week.
Chart positions tell you little as it can take as little as 5,000 unit sales to get in the UK top 10, hence why any title heavily bundled (like Horizon 3), spends months in the top 20. The telling stats are PCars 2 underperforming versus the original by 74% 1st week, and another 50% drop 2nd week.
Forums polls and post are a self-selective group so give a distorted picture versus the wider market. Forza 7 launched today and is #3 on Amazon UK. GT Sport is a little over 2 weeks from launch and has two sku's in the top 20 (#9 & #18). The others mixing it up in the top 20 are the usual suspects like FIFA 18, Battlefront 2, Shadow of War, Mario Odyssey and CoDWWII.