At High downforce tracks with shorter straights and lower power sensitivity MCL33 is capable of being on par with fellow midfield rivals. Poor aero efficiency means it falls behind on tracks with more/longer straights. Also according to McLaren an aerodynamic issue prevents them from making the car work properly in medium downforce configuration.
In short in Low downforce configuration there is too much drag, in medium downforce configuration the car does not generate enough downforce because of an aerodynamic issue which they cannot fix this season.
I kinda thought that this is the case, but pleasantly surprised by the difference between SPA and MONZA. At Monza OK, just on qualifying, Fernando Alonso was on 13th. Not bad for your description, and my expectation.
I whole thought it might be 17 or 18th like FP sessions. Kinda thought McLaren put something out of their bag finally.