After doing some serious research and thinking into the game, and having completed a "low" level run of the main game (Dr. Light's story at least, which I think is the hardest of the three anyway), I'm finding that the pros and cons of using Copy Core robots versus other elemental types really makes using the Copy Cores not very appealing, especially once you have tons of Starforce. Neutral types don't benefit much from Starforce (sure, the attacks are stronger, but they don't get the added damage benefit unless they use a Core, and in Player Battles you can't use items anyway), and the Neutral abilities like Mega Slide get outclassed by even Tier 1 abilities like Thunder Strike when you have a lot of Starforce. Sure, Mega Slide is one of the fastest attacks in the game, but you can't even deal triple digit damage to a 9999 Defense stat robot, whereas an ability like Bright Burst has that chance of a one hit disable. When you're up as high as I am, you're lucky if your AI-controlled active robot survives the first attack by your player-controlled opponent, because the Starforce is really with them (ok, yes, I did intend to use that bad pun, shoot me). So the benefit of having multiple different elemental attacks just doesn't seem to be enough, when you can have an entire team of elemental Robot Masters that can cover each other's weaknesses. Another problem is WE: it costs much more WE for a Copy Core to use an elemental ability (some even as much as 8 WE per usage), than robots that aren't exactly the same type as the ability itself. An example is Fire Chaser. Mega Man needs 8 WE to use it, but Quick Man and Top Man, who aren't Flame Cores, can use the ability for 4 WE. So ultimately my suggestion is to buff the Copy Core robots in some way to make them a little more appealing when you have so much elemental power to use and to deal with. So here's a few that come to mind:

1. Allow for Neutral Starforce to exist. These don't have to affect the Boosters and Breakers and Swaps and such, but allow Starforce to buff attacks like Mega Slide and Proto Strike. If they can be powered up to be a bit closer to how crazy powerful the elemental attacks get, I think the moves would be worth keeping in player's lists of moves.

2. Reduce the WE needed to use abilities for Copy Cores only. Copy Cores are using more WE for slightly weaker attacks. I cannot think of a Core out there that needs 8 WE to use an ability other than any of the Copy Cores.

3. This idea I like the most: give the Core items that can be obtained an additional purpose. Copy Core robots can get a slight boost in damage on certain abilities depending on how many Cores they have of that element. If a Copy Core robot has 49 Flame Cores, give that Copy Core robot half of a damage bonus as a regular Flame Core robot for using Flame abilities (whereas having 99 of an item ensures a full damage bonus like other robots). Half that bonus amount further if the selected ability is a dual-element ability so that some abilities don't get too powerful, or don't reduce it to make those 8 WE abilities worth the risk to use. The numbers can be adjusted as needed, I'm just trying to explain my idea.

Starforce hunting is a very rewarding side quest to do, but I've been finding that the idea is kind of making the game more unbalanced as the Starforce grows larger. We need to make sure that the robots that can't benefit much from it can still keep up without making them too over-powered at the start. Ultimately a team of elemental robots is still the ideal in fights, but we want ALL robots to have a chance out there, do we? Even if my ideas are rejected, I still hope that this problem is considered at least.

Something funny I noticed while beefing up Hard Man.

I know very little has been done about them, but what about the Genesis Unit? Ironically, you actually encounter them in the games just after the MM3 robots...but yeah, I'd say MM5 should be the main focus for now.

EDIT: Actually, question time. What robots are intended to be boss characters? The Robot Database says it lists robots currently unlockable in the Prototype. Will there be a database for Boss Robots later?

I got 9999 experience, btw, in a Fusion Star battle just by having tons of Starforce. It's really easy to level up the Electric, Fire, and Cutter Core robots now because those elements are dominant. No messing with Field Modifiers, no specific ability against a specific robot, just a good old fashioned battle can yield that 9999 experience. I got pretty much all of my MM3 robots leveled up to 100 in just a few battles.

To make things even more complicated with the story, there's reference to "Bass" and "Proto" units (I didn't see a bio description for Mega Man...). So maybe it is more of a simulator that Light, Wily, and Cossack got trapped in.

Any Neutral Attack will work. Heck, I think Proto Strike might be the most damaging attack of the Neutral attacks. What is more important is if you're on the home field of the RM you want to unlock, though. You face other RMs when you're going after Starforce, but you can't unlock them if you defeat them there instead of on their home fields. Just keep that in mind when you're trying to unlock all 38 Robot Masters currently available in the game.

I'm pretty sure that's yes for those questions. I used Mega Slide myself to knock out the MM3 RMs and got them.

EDIT: What RM were you trying to get? If it was a MM3 robot, you need to beat it on its home field to unlock it.