I'm not sure that's entirely true, XC race bikes run steeper head angles and less travel, where they still exist, than what you've nominated. Trail oriented hardtails certainly run slacker and with more travel than what's on offer here, but I'm guessing that's not the market for this model.
It would be interesting to see a carbon, trail style hardtail with slacker angles and a bigger fork.

Thank you for the recommendation Deem, Sounds like I owe Zeus an apology and need to reconsider my geometry preferences. That tantan FM199 you're happy with has a 69.5 degree head angle (when using a 496.3mm fork).
Doing some very basic maths, with the rule of thumb approach - 10mm A2C change = 0.5 Deg head angle difference I get around a 1 degree reduction from published with a 120mm suspension fork (Manitou R7) and approx 1.75deg increase in head angle when using an SP Cycle 471mm rigid fork. Either the Carbonada Zeus suggested or Deem's TanTan (Actually a little slacker than published due to the reference fork length) give a head angle around 68 degrees with an R7 and 70.8 with a rigid option. This seems a pretty reasonable switch between modes.
For reference, the SP Cycles M06 starts with a 67.9 HA which drops to 67 even with an R7, but only steepens to 69.7 with the rigid fork installed. This seems great for a hardtail, but maybe not quite steep enought for gravel racing?

48 tooth ring is too big for me, we've got hills and I'm no UCI WC level rider, aka, I'm not that strong. I think I'll start with a 38 and go up (or down) from there.

p.s. does anyone know how to insert a libreoffice spreadsheet table into a forum post?

I've been looking for a hardtail frame that has modern geometry (slack head angle primarily ~68deg). There seem to be a few on the market lately and I've been looking at the ones from SP Cycle. Can anyone tell me what the difference is between the SP Cycle models, M05, M06 and M08? other than aesthetics of course. Other than some very minor geometry differences, they seem very similar. What am I missing?
If anyone has a recommendation for a hardatil, I'd love to hear it.
I'm planning on swapping forks between rigid option and a manitou R7 to swap between gravel and mtb trails.
Cheers,

https://www.sp-cycle.com/2022-New-275er-Mountain-Bike-Carbon-Frame-EPS-Technology-275-Boost-T1000-Carbon-MTB-Frame-Size-135-15-17inch-p3814880.html?srsltid=AfmBOoordCDVdn4jqwv9PvfDz0l40lJTimm4zWzwxemwdF3hunT3KaKk

I've built one and it seems to be a really good little bike.