You are confusing facts for opinions my man. Liking or disliking a car's color or design is an opinion, because it depends on the person. You can have an opinion about that.
However, you can't have an opinion about how much faster or slower a car is compared to another. It's like saying "in my opinion 2+2=5". It's nonsense. McLaren can be either faster or slower compared to RacingPoint. It is going to be one or the other. There is no opinion on this matter.
The fact is, McLaren was the slower car compared to RacingPoint. You can say that the team performed at a higher level, they maximized their results, and made fewer mistakes throughout the course of the year. Nobody is discrediting any of that from McLaren. But the car itself was on average slower than the RacingPoint car. And that is a fact. Again, there is no opinion on this matter.
And to be absolutely precise, McLaren was on average about 0.1% slower than RacingPoint last year. If you need convincing, just look at this chart: https://i.redd.it/qbiw9i1nvr461.png
And an extra note: That 0.1% deficit is the average value. If you take the standard deviation into consideration, then the gap from the race to race turns out to be worse most of the time for McLaren.