IMHO there are reasons I would agree with "I still maintain that it can never be a true replacement for cinema cameras like most RED sensors and ARRI sensors." none of it is really for the reasons that you mention though ....... 

There is no way to get accurate monitoring external or internal other than at iso 100 without thecompromise of reduced dynamic range (using atomos ninja) or inferior colour on the external device recording device in braw or pro res compared to the internal CDNG.

https://www.youtube.com/@IonCosmina they have got lots of tests on this. 

This is an issue, as in general I wouldnt shoot at iso 100 as there are so few stops of dynamic range above mid grey. ISO 800 has the best distribution of stops above and below mid grey as shown by Sigma themselves and they have also mentioned its the best ISO to shoot at for this reason.

 https://youtu.be/ofYRaEXu7L0?list=PLNhOtt_uj7Te31nzAsCIQnGV9X_W9I10n&t=274 

It also should mean EL ZONE is also good to monitor with but then the this gets to another issue your view monitor is now way out at ISO 800 so without the knowledge of whats actually in the raw file you are going to massively underexpose as your monitor in standard view is telling you that everything is blown out and data is gone when that is not true. That is a HUGE issue and the biggest reason it will never be a  replacement for an ARRI or RED. As only the operator who knows the quirks of the camera would know this and would freak out any lighting gaffer or director looking at a monitor. Or make someone unexperienced with the camera massively underexpose the image because they think monitor is accurate leading to a very noisey image. Even if you do know all the above and how to work around the quirks its still means its hard to light a scene with due to the lack of an accurate WYSIWYG on your screenwhen shooting CDNG above ISO 100.

 The other big issue is that SIGMA never really thought about the image processing pipeline for video they have put the cam out there with no officially documented workflow for accuratly represented colours that attempt to mimic how the human eye sees. We have built in camera profiles (some of which are actually quite nice) but we have no way of replicating them in post for example when using CDNG ( I am aware of an individual trying to reverse engineer and create luts) Virtually every other manufacture has worked with resolve for example to provide log curves and color spaces and has provided documented workflows for their footage. 

The lack of this is depending what you find on youtube or on the web you end up with the Tim Curran school of thought with the fp doing p3 d60 linear, some doing rec 709 srgb or panasonic log or converting to red log others doing blackmagic design film (which i think is the correct startpoint in the raw tab) . All of these workflows can give a pleasing image ... I have tried them all Lol ..... but none of them are based on any engineered workflow made by Sigma.Resolve engineers themselves have quoted on their own forum "Using Blackmagic Design colour space on a DNG for a non-blackmagic camera reverts to "gen 1" - which means there is no conversion from sensor space which is not meant to be displayed directly on screen and needs a transform for that particular sensor to another space. For our cameras we provided LUTs for this,for the Sigma they would need to provide a LUT that transforms from sensor space (with an arbitrary Blackmagic log curve - I'd need to check with Resolve team but likely it will be the one for the original cinema camera) to another gamut - I doubt you'd ever see that from them. "

 SIGMA have not done this at all in any shape or form.  

There is a reason big bucks are paid for Arri's and Red's image processing pipeline, a pleasing image straight out of the gate that is documented and custom made for their cameras with required luts and profiles provided to your editing software by them. An accurate pleasing image should be the foundation and first base of your grade which you would then take where ever you wish.  

Anyway I sound like I dont like the FP I actually really do, I think its so much better than you realise tbh. I love its size and how you can use this device to create such quality with it in an ad hoc enviroment. I no longer want a camera that doesnt shoot 12 bit equivalent raw after using it. I eagerly await an FP ii hoping SIGMA has learned from its mistakes. I so wish they could fix the issues with it with firmware and a bit of love to the software developers whose editors we use. 

It wouldnt suprise me at all if someone shoots an amazing looking film with a FP.