It’s a bit of both. Infants have more neural plasticity as others have mentioned, so when using the same learning strategy babies are going to learn better. That said, adults have a lot more knowledge and experience and are able to make connections to a lot more things; so there are methods aimed at teaching adults that are more effective than methods used to teach babies.

I can’t say for sure whether or not this particular study used proper testing, but as a whole introversion and extroversion is not pseudoscientific.

Jung wasn’t a good scientist, but he did a lot of studies and came up with a lot of theories, some of which happened to be at least partially correct. Also, you seem to be getting something mixed up because Jung defined introversion as an “attitude-type characterised by orientation in life through subjective psychic contents”, and extraversion as “an attitude-type characterised by concentration of interest on the external object”, whereas the more common energy focused definition is not from Jung at all - at least, as far as I am aware.

The big five personality traits, namely openness, conscientiousness, extraversion, agreeableness, and neuroticism have been shown to be consistent, even cross culturally.

There are limitations to that: like how it’s an empirical observation, that other personality traits exist that aren’t factored into those five, or that it’s possible there are a larger number of smaller subfactors that make up those five traits, but ultimately they are scientific.

I’ve found it easiest as a two step process, first removing all the vines using loppers (the kinda bolt cutter looking things), and then once that’s all been trimmed close to the ground and all the vines discarded, then using a normal shovel to uproot them.