How Random are Equipment Rewards in Smash Bros 4

Consensus appears to be that in Smash 4 all equipment reward possibilities are completely random, but there are special rules:

The rolling reward ticker appears to reward players based on what stage they are fighting on.

You apparently are more likely to receive rewards for the character you are using. But there must be some caveats to this, as a player who almost exclusively uses DeDeDe I seem to have mostly sword/glove/badge items.

There is general consensus that the higher difficulty you play at, the better the rewards you get. So, instead of a 100lb Hammer you might get a 100ton hammer.

Has anyone delved deeper into the reward system to determine what the likelihood of receiving different types of equipment or custom moves actually is?

For example, how likely is it that I get a custom move that I already have, for the character I'm playing with vs one I don't have yet. What about the characters I'm playing against? Or the stage I'm on.

I've noticed a lot of strange things. For example: I thought it was impossible to get duplicates of custom moves, but I've received "Top Spin Gordo" at least 3 times, but I still lack the 3rd Gordo customization. I've also received every type of defense equipment for DeDeDe, but none of his attack equipment.

Do I have to play above a certain difficulty level to get certain kind of rewards? Is Beam Sword only obtainable at 7+ difficulty, or only in Tour, or only in Trophy Rush?

I'm not trying to ask multiple questions here, but is there any higher understanding of how the reward system works and how to obtain specific types of rewards?

EDIT:

I've made a few observations:

1. Target Bomb seems to be prone to granting custom moves with the character you are currently using.
2. Trophy Rush seems to be prone to granting duplicates of custom moves.
3. Classic is a toss-up. Difficulty level seems to only affect the number of rewards you get, not the quality. Custom moves seem to be rarer than equipment. Equipment seems to be more likely from the board you are playing on and the characters you are fighting. Speed/defense/attack equipment appears to be given out in a ratio 3/2/1 (I appear to get 3x as much speed equipment out of classic as attack equipment).
4. All Star gives you the same kinds of equipment regardless of difficulty level, hard gives you more equipment. This mode actually earns you more equipment than trophies, but the equipment seems to be based on the characters you battle. You're equally prone to collecting custom moves as you are equipment, and custom moves tend toward not being duplicates (till you get them all anyway, then it's of course all duplicates). Speed/defense/attack equipment appears to be equal.
5. Crazy Orders gives you a ton of equipment, but I don't have the custom characters to analyze the types of equipment you actually get beyond level 20.

In none of the cases am I seeing that better equipment is likely from any particular difficulty level. It only appears that you simply get more at higher difficulties, and thus have a better chance through repeating odds.

EDIT:

I've made the following further observations:

6. After receiving many duplicates of speed/agility related equipment I have finally received the first of said type with the "risky respawner" effect. This is the first negative effect I have found, and I appear to have earned it after earning 4 "safe respawner" items in a row (somehow 4 rounds of classic awarded 4 safe-respawner items).

7. After earning my first pair of "max power gloves" I went on to earn 2 more "max power gloves" with my next two rounds of classic. This is interesting because it not only is a 3rd level item, but it's an attack item (which I had not been earning). Since I am still using similar difficulty levels, this leads me to believe you simply earn better things after you have acquired more of a particular item.

So: Getting 5 safe-respawner items "unlocked" the risky-respawner items.
Getting enough speed/defense items finally "unlocked" the higher-grade attack items.