Do we know what's different? From the panda podium video I didn't understand what changed with the new erx (with the exception of the brakes but i don't think anyone had any issue with the brakes, I certainly didn't).

Hopefully they improved the mechanic design as well as the water protection ..... 
I was just thinking about your rear derailleur failure description (the one failing after some tough decent) if it's a smart idea to ride something similar on a MTB with all that mechanic shocks.
I don't think so frankly. If there's a general design flaw this kind of sickness usually gets the whole " product family".
 

I bought one black matte and one black gloss. I recommend the black gloss. Didn't entertain custom painting.
I bought airwolf bars via AliExpress because wanted 36cm width. Very happy with the bars. They're the T1000 or T1100 (allegedly) cockpit. Costs 75 EUR plus shipping so you will find it on AliExpress at around 100-120 EUR. From the airwolf store. Very stiff, look very nice. They also sell a carbon Garmin mount but these are standard sizing.

I designed and got car vinyl decals cut locally. To me the frame looks a lot like a Factor, so I hacked their font and in trolling Factor with tractor and facteur on either side. I've washed the bike many times now, those decals aren't going anywhere but they're reversible. Very happy with the format. It's fancy vinyl, forgot the name, any car nerd will know. It's outdoors resistant. Cost me a whopping ten euro to do the whole bike.

I've just placed an order for one of these frames, I've been dealing with Perry at Ican cycling whose been really helpful, his email is perry@icancycling.com

LT268?
https://www.ltbikes.com/index/products/view/id/21.html
Geometry works, just use a stem longer by 1cm.
I have one, love it. Photo from this w-e. i've put 3k km on it so far.
Alternatively, VB 268 (a bit lower stack, and the thread on the forum has quite a few people reporting problems, but i suspect they get ironed out over time).
Or the SP Cycle 025SL, but for a change, it doesn't look like an SL7. Geometry wise, it's close to what you're after. 30C max though.
Or Yishun R1058D, but also 30C only.
The last 3 are very recent models so you'd get the latest and greatest (hopefully / presumably) in layup, weight and so on. But I only have nice things to say about my 268.

i'm more in sometight with this king of "aero shape" head tube, like specy venge or new giant propel

I would try a different plug, they're very cheap on AliExpress. You may also want to try fiberglass cloth, you can probably find a roll in a local diy store for cheap. People have sometimes used that to create some friction with slipping seatposts. How much torque are you applying?