I'm just gonna throw this out there, I don't plan on coming back to this thread soon. Just hear me out.
For the sake of this rant, when I say 'OC', this also includes 'ponysona', and vice versa. I came up with my ponysona after going through a few RPs with different OC's that I made up on the spot. After a while, I noticed myself gravitating towards the same character more and more, and I eventually decided that she was my ponysona. I enjoyed playing as her because her personality and dispositions were very similar to how I like to play out an RP: calm, level-headed, and always thinking things through, with a few quirks that I can have fun with.
Creating a ponysona on the spot in my opinion, is a little more difficult because you WANT it to be a direct representation of yourself, and sadly, sometimes this leads to very god-mod characters that end up breaking canon.
In terms of your OC being overpowered, it is one thing to say that your character beat a manticore, but was defeated by it (x) number of times, does not overwrite the fact that he still beat the manticore. If your OC trained for four years and is able to do a sonic rainboom, the four years don't mean nothing, as your character is still capable of performing sonic rainbooms.
I recommend visiting
this thread and reading through all of the posts (don't worry there is only a few) regarding how players and mods view 'godmodding' and it's dirty cousin 'overpowered', and also their suggestions on how to fix it.
I will now use my OC/Ponysona as an example:
(I am going to skip all the stuff that is meaningless)
Talent: Needlework and Swordplay ( Simple and straightforward. Not too vague that it is all-encompassing , and not so restrictive that you can't improvise with their talents. )
Personality: A quiet pony with a calm air of authority, but will step down to follow another pony if she feels that they are more capable. Will not back down from conflict. Keeps to herself often. Empathizes with orphans and outcasts. Has witnessed many horrors at a young age and is hesitant to talk about them, usually becoming irritated if pressed on the subject. ( Not really as important, as this is how your character acts around other ponies. Just be careful that your character doesn't have what I call 'charisma cancer'. Think kinda like a Fallout game, you don't want it to be so low that the players start hating your character too, and you don't want it to be so high that you automatically assume that everypony will follow your lead. )
Unique Traits: - Has a condition with her eyes where her pupils do not dilate properly in the sun, causing temporary blindness and disorientation, resulting in her favor of nighttime activities. Wears a shader to correct this problem during the day.- Has a second 'presence' in her mind formed from the awful memories of her past. This 'presence' is nothing more than an alter ego that instigates mental conversations.( Kept it simple and easy to manage here. Notice that she actually HAS weaknesses that are unique and interesting, and affect how she can be played. )
I really hope that I was able to help in some way. For now, I'm out.