The configuration your fans are in makes very little sense as the majority of the cool air intake from the front is going to be immediately diverted and exhausted out the side. and the top, it will not travel deeper into the build.
The fans on the side are pushing through a rad though, so I can see the reasoning behind the setup...?...but I agree re. the cool air not making it to the rest of the components...the airflow through the case is pretty severely disrupted by the configuration.
If it's primarily and mainly used for gaming I'd swap the radiators, so that the GPU rad is in the top of the case and the CPU rad is in the side of the case; and I'd switch the fans on the rad in the side of the case to intake, just to help airflow through the system.
As for positive pressure reducing dust, this article shows it to pretty much be a myth:
Dust Prevention and Case Pressure: Does It Really Matter? - Overclockers ...but turning all the fans apart from those on the top radiator to intake, will vastly improve airflow and also force more air through the top radiator, which is potentially going to mean less work for the top radiator's radiator-fans, which potentially means less noise. If you swap the GPU radiator into the top of the case then that should be a pretty nice bonus.
Also, if possible, I'd lower the top fan on the front of the case, so that it avoids blowing onto the cooler assembly. Lash it to the case mesh with cable-ties if you have to. If you could swap out the two 140s for three 120's then even better.
If gaming, the GPU is by far going to be the hottest component, so putting the radiator in the top of the case will remove its heat from the build entirely.
And yes, there's probably not as much air getting to the motherboard components as there could be, but, from the look of the board, I'd imagine you have a pretty solid VRM and you've got a RAM cooler, so, that's not too much of a problem? Heat will reduce the lifespan of your components, but the speed at which hardware becomes obsolete, I doubt you'll be on that board long enough for it to really effect you? But that having been said, it would probably still be better to switch the fans on the side radiator to intakes.
Also, while you've got an AIO on the GPU, rather than having the airflow follow the path of least resistance through the back of the case, I agree with turning the extractor fan in the rear of the case to an intake, just to get some fresh air to the motherboard VRM and to feed the top radiator rather than having it compete with and/or starve it. If you could do that
and swap out the two 140mm fans in the front of the case for three 120mm fans,
and turn the fans on the side-radiator into intakes, then (if you move the GPU rad to the top of the case) you'll be vastly improving your airflow, and forcing even more air through the GPU radiator (assuming you've moved it to the top of the case), meaning the GPU rad fans won't have to work as hard.
But, if you only do
one thing, I'd definitely switch the rads, so that you can get the heat from the GPU out of the system entirely.