It’s an obnoxious feature, but it’s intentional. Not some kind of “this is old and therefore bad” thing.
Slot head tools/fasteners transit too much torque which often resulted in the fastener heads shearing off when used with power tools.
Rather than build a complex torque limiter into the tool (which would need adjustment based on use case), they built it into the fastener.
I hate Phillips Head screws, second only to flat head screws. They're "fine I guess" for some low torque applications, but even here they're not great. Was at GF's house the other day trying to screw through 18mm ply with some Phillips screws, which were all she had in the length I needed. Couldn't even get them through one sheet with predrilled pilot holes without them camming out and stripping the heads. Awful. Ended up making a trip to Screwfix to get some posidrivs.
"[..] and in such a way that there will be no tendency of the driver to cam out of the recess when united in operative engagement with each other."[1]
Wikipedia says:
"The design is often criticized for its tendency to cam out at lower torque levels than other "cross head" designs. There has long been a popular belief that this was a deliberate feature of the design, to assemble aluminium aircraft without overtightening the fasteners.[14]: 85 [15] Extensive evidence is lacking for this specific narrative, and the feature is not mentioned in the original patents.[16] However, a 1949 refinement to the original design described in US Patent #2,474,994[17][18][19] describes this feature. "
1. https://worldwide.espacenet.com/patent/search/family/0216985...
> Despite popular belief,[2] there is no clear evidence that this was a deliberate design feature. When the original patent application was filed in 1933, the inventors described the key objectives as providing a screw head recess that (a) may be produced by a simple punching operation and which (b) is adapted for firm engagement with a driving tool with "no tendency of the driver to cam out".[3]
> Nevertheless, the property of the Phillips screw to easily cam out was found to be an advantage when driven by power tools of that time that had relatively unreliable slipping clutches, as cam-out protected the screw, threads, and driving bit from damage due to excessive torque. A follow-up patent refining the Phillips screw design in 1942 describes this feature
Also Note: the opposite is not true. Tightening using and impact driver is a great way to cam-out and damage a Phillips head screw. That's why torx style is much more popular with impact drills.