The Japanese manufacturer endured its first winless campaign in 20 years in MotoGP last season as it tumbled down the order with an M1 bike which made little progress from its predecessor.
Despite having the benefit of concessions and bringing in fresh engineering talent from rival teams, Yamaha has done little to climb up the order in 2024.
After a difficult sprint in which he felt he would subsequently struggle to finish Sunday's grand prix due to tyre wear concerns, 2021 world champion Quartararo was a distant 11th.
Team-mate Alex Rins struggled to 16th on his Yamaha debut.
Assessing Yamaha's current standings, Quartararo was scathing about where he sees the Japanese manufacturer.
"Compared to how the level is right now, I would say yes," he replied when asked if this is the worst the bike has ever been.
"We improved, so this is something difficult to say. But the level of our bike compared to the others, it's true that we are further than ever."
He added: "We are further than last year. We have improved a little bit but they are even better and faster than last year.
"So, the gap between all the European manufacturers and us is even bigger – even to Honda it felt that today we were missing something, and they are also struggling a lot. But I felt we were even worse today."
Speaking to French media, Quartararo noted that he feels like he is racing in a "championship of the others, because honestly we're six Japanese bikes [Honda and Yamaha] and it feels weird that they are so far back".
Commenting on his race, Quartararo said he managed the tyre drop he feared by using a softer engine map.
But this only served to highlight that the Yamaha has no speed when the tyres are fresh and has lost a key strength in its speed through long corners.
"Basically, from lap one to the end I was with a totally different map, much less power, working more on the throttle connection to save the tyres," he explained.
"But I mean, it was still very difficult to do it. I don't know how I managed to get 1m53.5s in the end.
"But the problem is the potential we have in the first lap is slow. We are not able to go as fast as the front guys.
"I made a great start, I was behind I think Aleix [Espargaro] and [Pedro] Acosta at the beginning.
"But as soon as there are long corners with a lot of acceleration, which was our strong point in 2021 where I pulled away from the Ducatis in the triple right, it is now our weak point.
"So, that's why we are questioning ourselves as to why we are slow in these types of corners."
