WTB are not necessarily OEM rims.
There's the ST series, which is quite heavy ~500-590g a rim depending on size (507g for 29" 19mm i.d.). But they are meant to be durable with all the nice things like reinforced spoke holes, etc.
And they do the Frequency, which is their lighter off-road rim (417g for 29" 19mm i.d.). I have a set of WTB Frequency CX rims on my gravel bike. After 10,000 km I took them on the truing stand for the first time. They were only about .3 mm out laterally, easily came back to within ~.1 mm (yes, that may be over the top, and most people wouldn't bother with .3mm, but I tensioned spokes and while you're at it ....). Easy to set up tubeless as well (with a track pump), although I don't run WTB tyres (Panaracer GK SK).
If you only ride 40mm tyres, the most saving could be had going for narrower rims. 19mm i.d. is enough for 40mm.