Here are Autosport driver ratings for all F1 drivers since 2016 that have made their debut as a stand-in driver for someone else:
Bearman 10
Lawson 8
De Vries 10
Aitken 7
Fittipaldi 7
Giovinazzi 9
Vandoorne 9
Average: 8.57
Average for other drivers in the same races: 6.92
So stand-in drivers are on average rated 1.65 points better than regular drivers and it’s questionable whether in theory they would even deserve to match the regular drivers, because on average, stand-in drivers would be worse drivers than regular drivers, because there’s a reason for why they weren’t regular drivers at the time. Vandoorne, Giovinazzi and De Vries all got the chance to be regular drivers later in their careers and they were all rated below average compared to the rest of the gird when they were regular drivers.
So if you correct for that, I think stand-in drivers’ performances (especially if we are talking about rookies) are on average overrated by at least around 2 points, which is utterly ridiculous margin on a 1-10 scale. It just shows how biased these ratings can be and how much fans and pundits overestimate the difficulty of stepping in as a reserve driver and doing a solid job. I used Autosport driver ratings but this is completely in line for what I saw in official „Driver of the Day” votings, our Voting Championship on this forum and pretty much anything else. Just wanted to show you this, because while you could make a reasonable argument to defend each of those ratings in isolation, the collective numbers leave me in no doubt that there’s a huge and irrational bias favouring these stand-in drivers.