Essentially, my question boils down to whether or not my front chain ring is worn down and needs replacement. When I research these things online I can only find extreme, obvious examples of when to replace parts. Less obvious cases, at least to my untrained eyes, are harder to find. (Apparently I am not allowed to post photos here for others to judge.) The chain ring is certainly worn, but is it worn enough to explain my chain slipping problems?

For added context...

My bike is just shy of 2-years old with, as a very rough estimate, about 2000 miles ridden.

I let my chain wear way past the point when it is generally recommended to be replaced. As I understand, now, the rule of thumb is to replace the chain when it has 'stretched' about 1/16" past the 12" mark on a ruler (lining up the 0" mark with the center of a rivet, the rivet on a taught, new chain should be at the 12" mark). Once the chain gets to about 1/8", it wears the cassette to match the chain. Embarrassingly, I let my chain get to 3/16", so it most definitely needed to be replaced. To my eye, the cassette didn't look so bad, but my eyes are not well calibrated to spot such things so I decided to replace the cassette too.

As long as I was replacing the cassette, I decided to adjust the gear ratios to ones more to my liking, instead of what came stock with the bike. Originally, I had a 9-speed, 11-34T cassette but really only make use of the top half of the gears. So I replaced it with a 11-25T cassette, effectively loosing the gears I never used and giving me a finer transition between the gears that I do use, Since the news gears were a subset of the old gears, I kept the chain length (number of links) the same from before. So the things that changed are: new chain (same length) and new cassette (different gear ratios).

Now, after making the replacement, my chain is slipping like crazy when I pedal with very much force. It does not really slip when I'm watching it, so I cannot be 100% sure of what's happening but I think it is slipping on the front chain ring. Aside from the fact that the chain and cassette are both brand new, evidence that points to the chain ring includes the fact that on one of the big slips, the chain fell off the ring. Additionally, when I change to the biggest ring from the middle ring, the slipping does not seem to occur. (Out of my three front chain rings, I'd say I use the biggest ring ~10%, middle ring, ~90%, and the smallest ring ~0% of the time).