Others here will be better placed to advise on specific China rim brake frame options, but if it helps to inform your thinking then:

- unless you specifically want a brand new frame then well worth looking on EBay and other marketplaces for used rim brake frame sets. I’m guessing you might be in the UK (‘wits’ end’) in which case there are some really good deals to be had on eBay rn for out-of-fashion carbon rim brake frames. Probably true in other countries too.

- plenty of good reasons to choose a frame that’s compatible with existing components rather than one that requires you to start again. But worth considering st least if you’re likely to want to upgrade those components at some point - if yes it could make more sense to bite the bullet now. Debates about performance aside, disc brake bikes on the whole allow more potential for bigger tyre clearance (although the 32 on that TanTan is wild).

- if you’re riding your endurance frame slammed with a long reach stem (130+) then that suggests you could afford to ride a more aggressive frame, at the very least with spacers and a shorter stem. If you find your Allez too sluggish, too unresponsive, too sit-up-and-beg - then you may want to get a frame with a more aggressive geometry. If you like the characteristics just fine, then - based on what you’ve said - no great advantage i wouldn’t have thought.

- you don’t give much detail on the type and amount of riding you are / want to do. i’m currently 87kg. I’ve got race bikes with 25mm tyres and endurance geometry bikes with up to 33mm tyres. The latter type is definitely more comfortable but the former does just fine because they fit me. If I want to go on a fast club ride I’m on the race bike, for commuting and longer, more leisurely rides, I’m not. If I could only have one type I’d go endurance geometry - for me, the speed and responsiveness benefit of the race bike isn’t great enough to trump comfort.

Hope that’s at least marginally thought provoking. Good luck!

Idk your riding or your FTP, but as unit myself (c.83kg), i'd recommend a disc brake bike with 50mm wheels, 60 if you mostly ride on the flat. Wide rims, at least 32mm, expensive tyres, so you can really get comfortable (even a 28C tyres would measure over 30mm) & aero (no exposed calbes, integrated cockpit, 36cm bars...)
I've been recommending the LT268, very cheap. A bit dated, not the lightest, but fast. Or go down the rabbit hole of finding something newer, lighter, and for what price. It was the best option i found when i bought these frames in 2023, but many models have come out since.
I own a supersix rim with campag carbon wheels; discs + wide rims are a different world of braking performance, speed & and comfort.
In fact a friend of mine, same size, weight, build, is still on his supersix. Same tyres & tubes. Anywhere but on steep stuff, there's a 20+ watts difference for the same speed. Assumption: our power meters read the same (we never tested that). He's on Assioma and i'm on Vector. His all setup is anti aero, mine is full aero. When we go downhill the speed difference is absolutely staggering.
You can get wheels for 500$, and a frame for 500$. You'd want full hydraulic braking. So basically you'd have to upgrade almost everything.
But that's only my 5 cents

Velobuild was having a clear out of some rim brake frames, last time i checked. You might get lucky there.

I have branded disc brake version of LCR0X. You may go one page back to read my post.
1. The frame and overall quality was very good and I have no issues with the build.
2. Majority of the tubes have aerofoil profile instead of Kamm tail. It is not optimised for regular bottles so you may have to look for something like Cannondale aero bottles.
3. The saddle clamp looks ugly in my opinion but it allows for a huge range of adjustment and has a quite robust design in general. Seatpost clamp bolt located way too deep into the frame. During initial weeks of fitting i rode with long T-shaped hex key, as I couldn't reach the bolt with any of my multitools. Same goes for saddle clamp.
4. It's relatively harsh ride due to the seatpost shape and lack of sloping in top tube, but hey, it's an aero frame, they all are quite harsh. If you have decent roads in your area you will be fine.