Hmm..this topic is not really new and has been discussed in other forum many times actually... a lot of arguing, debating whether if IWC fully in house on those model you mentioned...
honestly, to me, i have been using few models and i found the built quality and the movement is really not bad regardless if it's eta based or not..
i owned a mark XVI, eta based, no problem at all, keep very very accurate time

I have owned 2 IWC 3717 chrono, eta 7750 based, no problem at all, both keep very accurate time too... one of it (3717) gain only 1 sec in 2 days....
Also, i have once seen (below pic) a IWC eta 7750 movement in their pilot range which has been adjusted to 5 position and it's engrave in their movement... it's not very well polish (is not see-through case back anywhere) but i can see IWC put a lot effort in to it...
for example: Pic borrow....


then of course the fully in house 5001/5004 movement... i have both port 7 and BP, both gain around 6 sec everyday.. but the gain is consistent.. i timed my port-7 for 2 months while i was in UK, consistently gain 6 sec everyday.. didn't really bother to time the BP that long period of time... checked once and it was around 6/7+ too... but of course, different people might have different rate... this rate is based on my wearing-style...
come to think about it, for a brand like this, i think not a lot can offer you a Mark XVI for 11K (retail), a 3717 for 14K (retail)... this make possible because they are still using eta-modified/refined-eta and if all movements are in house 100% by IWC, the cost sure shot up and i don't think they will still able sell at that price range... think about Panerai... their new in house model...all at least 25K about... sooner, you will not able to get one below 20K..
Just my opinion

Happy CNY (still... )
Scott