Guess what? So did I. So did most of us here.
With respect to "the decision to use predominantly humanoid aliens," the metric that matters most is time spent on-screen. What you're saying just isn't so.
Even Odo, officially non-humanoid, spent the overwhelming majority of his time on-screen in humanoid form. It's one thing to say that a species is non-humanoid, but it's another to show it. Q, the Organians, Trelane, the Thasians, the "Catspaw" aliens, The Kelvans, The Founders, etc. were all said to be non-humanoid, but the overwhelming majority (or all) of their time on-screen was spent in humanoid forms.
TOS had a fairly appreciable number of non-humanoid aliens. But if an episode required more than one of member of a species, the rule was that they were humanoid, and quite often they had minimal-to-no special makeup. Examples include (but are not necessarily limited to): "Journey to Babel," "A Taste of Armageddon," "A Piece of the Action," "Patterns of Force," "The Apple," "Gamesters of Triskelion," "The Omega Glory," "The Mark of Gideon," "Wink of an Eye," "Bread and Circuses," and "Miri." That's just off the top of my head.
In "Arena," we see two new species, one instance of each. One is definitely humanoid (The Metron), the other is a person in a Gorn suit. Is the Gorn humanoid? It depends on how strict your definition is.
If we take a look at "Day of the Dove," you have one pinwheel alien as an optical effect in certain shots on one side of the scales and a bunch of humanoid Klingons, often in the same scene with the pinwheel, on the other.
Then, Spock is in every TOS episode and getting a lot of screen time.
In "The Cage," you have at least four humanoid species: The Talosians, the Kalar on Rigel VII, the Orion, and the Vulcan. The person in the bird suit is arguably non-humanoid but is barely visible.
The non-humanoids are certainly there, but they don't appear on-screen in as great numbers or for as much time.
I could go on, but I'm reluctant to invest in making a chart of aliens when there's little doubt (IMO) that the humanoids are going to win the contest of which type of alien had
the most visible screen presence on TOS (or any of the other shows for that matter).
Seriously, look at the Xindi. Most of the time was spent with the humanoid varieties. Despite that, it was impressive that they pulled off the scenes with the Aquatics and Insectoids as well as they did. It's also somewhat amusing that they conveniently made what would arguably have been the most problematic to do justice to, the Avian form,
extinct!
But not as crewmembers or regulars.
Exactly.