Yes, it is scientific, but bodybuilding is also very individualistic.
Everybody responds differently to different things.
If there was one “magic formula,” then everybody could be a champion bodybuilder.
If you followed EXACTLY the same diet, training, and drug cycle that Arnold did back in the 70’s, you would still not look EXACTLY like Arnold did.
Genes, biomechanics, body frame/structure, responsiveness, etc. are at least a little different in everyone.
It’s about finding those things that work best for you.
Hence the conflicting opinions on what works best.
When a veteran trainer tells you HIT or whatever works best for them, it probably does – for them.
Other things may (and do) work better for other people.