To be clear: ALL of the OEM PCVs have the same inherent weakness (without the Venturi).
The intake blue path vacuum source goes away when you transition to throttle, and relies 100% on TIP vacuum at that point. If it's not strong enough/available, the crankcase pressure rises due to blow-by.
When crankcase pressure is closer to ambient pressure than it's target vacuum (roughly -0.9psi ish, depending on the specific valve), the diaphragm must open up in order to try and allow the vacuum source (TIP) to draw down the crankcase. This is just how a simple regulator works. That's all that the diaphragm is.
This CAN happen with stock tune, stock TIP, stock turbo, etc etc. It's just far HARDER to make it do so. I think it requires TIME of running with the crankcase depleted for the oil to surge upwards. Longer RH sweepers with part-throttle is going to be the worst part. Rolling onto the throttle slowly (like you do when driving on track at the edge of traction on corner exit) doesn't allow the vacuum to build quickly enough, meanwhile RPMs are high, and when you DO get WOT... there's a sudden hit of boost, pressure in the crankcase, diaphragm is wide open... and then hard suction builds and pulls a volume of oil with it.
As far as the effects of a tune:
When you tune the car you are messing with 3 main things:
1. Blowby. Boost hits harder at lower RPMs. I cannot measure this, but more blowby is reasonable to assume. How much... don't know.
2. TIME. It takes TIME to draw the crankcase vacuum down to acceptable levels where the diaphragm closes. This is why the one TIP can't even generate a vacuum in 2nd gear, but can generate about half of what's needed in 3rd. It's not blowing through the RPMs as quickly so it spends more time with a draw on the TIP that can do work.
3. Little more vacuum draw. This is about the only good thing. BUT it doesn't happen fast enough to counter the big hit to crankcase pressure on initial spool.
Here is a stock TIP, stockish boost levels vs stock TIP, upped boost levels. Basic retrofit (no venturi). This is the exact same effect that'll happen with any of the OEM MK7 valves as well.
Obviously with 10 more psi of boost it's going to be a lot faster. But with the two graphs matched at the same RPMs... you can see that the crankcase isn't getting drawn down appreciably faster. If you look at the PCV vacuum source, there IS more of that. But it doesn't really make a difference before it matters.
edit: and just for funsies... here's the low boost/"stock" boost levels vs the higher boost tuned + Venturi... it keeps the crankcase under control as soon as boost is fully built.