I would never use wood to hold a car up. 2 x 4 is made of pine, which is a very soft wood. Is your life, or one of you friends or families life, not worth the extra money to buy a good set of jack stands??
Nothing wrong with a good design of wood blocks. (pic would help) Not sure what type you're referring to, but just like anything else design is as important as materials. I trust my wood ramps ( 2x6 to 2x 12 pt construction) more than old cheap rusty steel ones. They have solid wood that can't compress or twist sideways where weight rests. Same with resting car frame on wood, I use large & wide enough scraps of pressure treated wood that they are actually more stable than jackstands in the event of car being bumped hard or something. Seriously, people have bumped cars on jackstands with another vehicle resulting in injury or death. Sad but true.
Also , particularly on very poor concrete, or dirt, jackstands are an accident waiting to happen. Seen that too many times also.
Anything wood I use is pt so it won't rot and ends up being way the hell heavier than a steel part. Most yellow pine pt is not exactly what you'd call soft like the cheap spf (spruce/pine/fir) genetically engineered fast growing crap 2 x4 interior wall material is made from. I'd agree with preferably not using that crap. Anywhere I use a screw , I predrill holes to avoid splitting.