Ugh... FFS guys - wheel company here: people break both types of rims.
As for which one is stronger? Tubular. No question about it. Not even close. Tubular is stronger and more durable. You're also more likely to finish a ride on a cracked tubular than a cracked tubeless wheel. The reality is that even with a cracked rim on a tubular if your tire is fine then you can keep running it. I've seen rims with small cracks in them run a whole season of racing.
Tubular as a technology is still by far the best for cross. 2 things always stick in my mind: Sven Nys telling us, "I start at 1 bar and go down from there" when asked what pressure he ran and Katie Compton coming through the pits at nationals and telling mark "9". She meant PSI. She won. Tubeless doesn't work in those situations so those running tubeless must run at higher pressures. Running at higher pressures and using stiffer tires puts them as a great disadvantage.
Yay. No one here cares about that though. Road tubular? Sure. Whatever. I have stacks of rims sitting here if anyone wants to ever build anything again. Until then I will keep building them for track and cross.
If you don't understand tubular or think it's time is done then this thread isn't really for you anyway.