What I think is also lost in these debates about grinding is that, at least within GT Sport, the 20 million credit cars were a concern, but were ultimately immaterial to the game. They served no real use in a game ostensibly about online racing, even as Polyphony bolted on a single player that ultimately didn't matter either.
However, it matters here, because these 20 million (and hell, even some of the more prized supercars) cars have an actual use case in the single player, and presumably in online races too considering the open PP nature. The single player suite is the star draw here, not the online. And it's clear to my mind that Polyphony designed the game's economy to be based around scarcity and skimpiness (whether that ultimately came from wanting to base it around MTX's day one, we'll have to see)
There's also the elephant in the room that the game, by Polyphony's own admission, was designed around car collecting. They wouldn't give you a scrap book with the game's full car list in order to not do that very act, they certainly wouldn't give you Menu objectives that basically revolve around 'buy from the Used Cars, or win specific cars from one off races' if the game wasn't built around collecting cars. It's certainly a hell of a lot harder when most of the high grade cars are locked behind massive credit caps when money is tight, when they rotate in both the Legends Cars, and 'by invitation' in Brand Central, and when cars in game have generally inflated massively in value (in the case of the 90's JDM heroes, AKA the entire calling card of GT to some, you can only get mileage examples from Used Cars)
So yeah. I certainly think that compared to other games, GT7, and Polyphony, should be raked over the coals for the almost ludicrous amount of grinding. And why I can't help but wonder if this was all designed to be that way.