The difference in negative dust intake and positive dust repellent is negligible. The dust filters will only keep out the larger particles, the finer stuff still comes through just as normal.
Almost all prebuilts use a primarily negative system, as do many cases such as the NZXT 510 series. There's also a few cases like the Fractal Design Meshify-C that use primarily positive.
Either way doesn't make much difference overall since the case is not sealed and the differences are minute. Linus did a 1 year test covering 5 different fan layouts in Fractal R5 from all negative to mixed to all positive and his conclusion was you still got pretty much the same amount of dust intake, it was just deposited and concentrated more in different areas of the case, depending on which layout was used.
You can have 3x fans at intake and a single exhaust and still be negative. The exhaust creates a low pressure area directly adjacent to the blades, but covers an omnidirectional arc, it'll pull from the nearest available source, which is generally the gaps/venting right next to/above the fan. It's only when the 3x intakes can provide overwhelming pressure from high rpms where the gaps/venting gets swamped, that the exhaust will pull from the case more.
The fabled 'smoke test' video is a joke. The author didn't take into account the gpu fans which in the case of the NZXT 510 and many other cases, use those rear gaps as an air source, providing better airflow and temps all around than the use of front intake fans can provide.
Pretty much unless you only have intake fans and a 100% positive setup or fans at a constant high rpm, all cases will run negative pressure at idle/low rpm. The front intakes at low rpm simply do not supply high enough cfm/sp to compensate for the amount of volume of air that needs to be moved for front supply to actually reach the rear.