It is critical to focus on technological node here, SMIC is expanding 14-28nm capacity, not sub 7nm capacity. The latter at the moment cannot be built in China.
They cannot focus on both expanding the 14-28 nm capacity in China and sub 7 nm capacity elsewhere because their budget is limited - they are unable to dish out $40+ billion figures like TSMC since they are still much smaller than them. This is especially true for advanced fabs since the equipment is very expensive, so unless a European partner in JV would be able to weather all the costs, this would inherently hinder SMIC's expansion of Chinese fabs.
I agree that a JV endorsed by European Commision is a must, otherwise the project is doomed to fail.
I don't agree that this would be impossible to achieve. Of course US has strong lobbying in Europe Commission, but as I said there is not a single voice is Europe. The outcome of this attempt, indeed would be very uncertain....it can go both ways, it is impossible to know for sure now.
The thing is that semiconductor supply chains are now deemed a national security level type of thing for many countries, so for any cooperation, there needs to be mutual trust. The latter is on one of the lowest points right now. For example, take CAI which was frozen recently by the EU - it was pretty beneficial for the EU but politics won in the end. I think the same is going to happen with any semiconductor JV, especially if it is going to involve a black-listed entity like SMIC - I think there isn't much incentive in both Europe and China to engage in cooperation on something as important as semiconductors.
I agree that it would be very difficult for Europe to build a 5nm fab all by itself, but this is a very good advantage for SMIC, because it can offer something that Europe alone cannot and this has weight for discussions with EU commission.
Regarding who benefits more, with all the due respect, this is somewhat a bit shortsighted, SMIC should see what advantages they have, and I guess they have a lot, but even more advantages has the vast chinese fabless ecosystem, especially in AI and other advanced technologies because they would have a trusted supplier. In my opinion it is much easier for US to block TSMC or Samsung than blocking an European JV strongly endorsed by European Comission.
There won't be much difference between TSMC, Samsung, or SMIC's JV with a European company for the Chinese fabless companies because the fab would still source equipment from the US and that is covered under the US tech export regulations - meaning that any Chinese company could be arbitrarily black-listed from such a fab just like with TSMC or Samsung.
It is not a jab at the EU btw - the same would happen in China as well if the fab sources the equipment from the US. It is one of the key missions for China is to achieve satisfactory levels of self-sufficiency across the whole fabbing process - from lithography to EDA so that the geopolitical risks from the US sanctions are minimized. Therefore, unless China or\and the EU gain enough self-sufficiency across the whole spectrum any advanced fab would be essentially the same as TSMC\Samsung ones in terms of risks even if the EU and China are on board with it.
Finally a brief comment on times. I think achieving state-of-the-art 5-10 years sooner it makes a lot of difference. What US is trying to do is to slow down China, not to stop it, because they know it's impossible, but for US also slowing down of 5-10 years is a big win, and actually it is. For them it means to have the time to prepare themselves and be ready and reaming ahead of China when China reaches EUV.
The JV fab with a European company is most likely going to take as much time as the current estimates for Chinese EUV, if not longer. It would need to go through the approval process and that is already going to take quite some time with all the political things that are going to inevitably arise and the US pressure. Let's say it passes, picking the location and building the fab is also going to take several years - e.g. TSMC's US fab is expected to finish in 2025 if I remember correctly, and they already started. So for SMIC JV fab, the lead time to establish a 5 nm fab is probably going to be around 2027-2028 if they start right now.
Your proposition is good for discussion and I see your points but I think that at least for now it is not possible to be used in the manner you proposed - as an EU-based fab that would primarily service Chinese fabless companies - because of the reasons I listed above (after the 3rd quote of your post) as the main risk lies not in the TSMC or Samsung as companies but in the US equipment providers.