The point of this piece was to serve as a rebuttal to the handwavy notion that design is purely subjective. Of course design has subjective aspects—humans are subjective creatures, and we design for them. You're spot on with the statement that professionals have the approaches and tools for evaluating design choices.
The little-league-ers, in my experience, rely on subjective statements ("It looks / it feels") more often than the ones who have depth. As a designer, my responsibility to my client is to be able to explain why my choice is in service of their business goals. More often than not, it sounds like a chain of justifications up the hierarchy of needs. Sometimes it's a conscious choice that is worse because something else has higher priority. It takes some practice to articulate, but there's rarely a choice that isn't related to your other choices, which are in turn related to your constraints. If you can't tie a choice to that chain, then it might just be that it doesn't matter, but more often than not it's a red flag that your choice isn't grounded in conscious thought about what makes your thing better.
* "UI/UX is purely a matter of taste in much the same way that cooking is just a matter of taste."
* "If you meet a fellow who claims that design is subjective, tell them that they’re right, if they choose to work with the little-league practitioners."
And the former seems like the stronger of the two statements. It seems true enough that the usability/experience fields, like cooking, have a body of theory and research that professionals can draw on to execute a "vision" consistently and effectively. Yet cooking is still significantly subjective. Professionals can and do disagree on whether a given vision is desirable. Individuals can be constituted so that what might seem familiar and desirable to one might be experienced as strange and unpleasant to another -- for example, the taste for cilantro seems to be more or less genetic.
You might argue "well, what's meant here is that UI/UX professionals are aware of this 'subjective' aspect of the job and in fact have approaches and tools for dealing with it" ... and again, that seems true enough in my experience, but that's a different statement from saying anyone who claims that design has significant subjective aspects is only working with little-leaguers.