Chinese titanium

Buy a used Litespeed or Moots on eBay.  You might have to wait for one you like or your size, but at least you'll know its pedigree / genesis.  My Litespeeds have a lifetime warranty and have been hammered, truly hammered on sportives like Paris Roubaix - several times: no issues. 

A name that seems to crop up a lot in relation to this topic is Watly. They offer custom geo, so a horizontal top tube is certainly possible. I do know that you need to know pretty much exactly what you want, though - they ask you to fill in a spreadsheet, basically, and they make the bike to your specs.

This might be interesting: https://mamilmusings.com/waltly-titanium-frames-review

see also https://weightweenies.starbike.com/forum/viewtopic.php?t=134517

There are numerous threads on weightweenies and LFGSS about Watly and Chinese Ti in general, with other recommendations.

In brief, it seems to come down to this: great frames, by and large, if not finished to the same kind of standard as an Enigma or similar. Quite how you'll get on if there's a warranty issue is an open question, and that is always the difficulty with any kind of direct from China bike (whether Ti or otherwise). I would treat the purchase like a second-hand one, and assume there's no warranty. If it still seems like a good buy in that scenario, then go for it.