I can actually agree with a lot of what you said.
I love the DKC games. I never really analyzed the level design, and I never compared them to Mario games for example I took them at face value. What that boiled down to was, 'is this game fun to play?' It was (and still is).
However, after reading your analysis I can't help but agree with you on most points. The enemy placement is arbitrary. The level design is random, and heavily recycled. But, also, with only a few choice exceptions, this was just the way games were back then. At least platformers. They were all extremely linear, with no real rhyme or reason as to why there was a jump here, or a floating platform there, or why this enemy just walks back and forth on top of this random horizontal surface, or why that enemy just flys up and down in this random vertical path, aside from the fact that I need, for whatever reason, to cross it.
They were designed primarily to look good, control well, and offer a challenge. Not to be traversed with a semblance of natural progression and realistic terrain. No, you just walked right until you had a dead stop with a boss, and defeating him somehow meant that just beyond him, it was no longer a desert, but a volcano, or an ice world, or whatever.
So, while most of what you said is true, it's not really a fair way to critique DKC. Because the same could be said of many games, Sonic, Mario, et al. included.
Bottom line: while shallow, it was still fun.