It's not contradictory.

I'll give an example: Landmines are a good tool for slowing an enemy army. However, if your military consists of *just* landmines, it won't be very effective. That doesn't make landmines a bad tool. Indeed, even a super-weapon, like the first jet fighter, won't win a war if it's your *only* tool.

Learning -- even a language -- is a complex process, and you need many tools. Spaced repetition is awesome for factoids. If you want to learn a language, you need to memorize vocabulary. SR is great for that. If you add 5-15 minutes of spaced repetition to a good language program, it will help a lot. If that's where you spend a majority of your time, you'll learn very little. However, SR won't help you practice a broad range of skills around listening, speaking, understanding communication styles, or quite a few other things.

Ditto with physics and math. If you know equations, it accelerates everything else. However, the bulk of the knowledge isn't factual or procedural; it's conceptual. Simply memorizing formulas won't help you. On the other hand, in most cases, once you learn conceptual knowledge in physics, you never forget it.

"Coding vocabulary" isn't in my top-50 problem with junior developers. Naming variables, algorithms, systems design, etc. are. Most of those don't align to SR. I'd take a programmer who spends 8 hours coding over one who spends 8 hours memorizing library calls in an SR system.

Note 2:

The spacing effect is /somewhat/ broadly applicable (but far from universal), but spaced repetition specifically is only helpful for factoid-style knowledge. You can look over the different classifications of knowledge, skills, and abilities (factual, conceptual, procedural, declarative, etc.).