I would be fascinated to see your data... seriously. Please post the results of your tests. Because others have tested this extensively and come to the opposite conclusion. Including - for what it's worth - people who work for Konami (who heard about this crap years ago and checked it out, just in case).
Look, I'm not trying to be snarky, but every year there are a couple of people trying to spread this stuff, and like it's a bloody plague. One game of PES is completely different to another, we all know that, right? Sometimes it's smooth as cream, other times you feel like you're playing on a swamp in a tornado. Same teams, same conditions, everything. It's all part of the "magic" of PES. Now, there are countless people here - as there are every year - telling you that what you're experiencing is just this kind of fluctuation in gameplay, and they've noticed no consistent problems with imported kits. None whatsoever. People like me, who are ancient, and have been playing PES games since the 1990s, and have heard this stuff year after year...
Well, a very small minority have "reported" this... and they've all been wrong. And what's more, lots of them have made completely nonsensical claims like "it defaults to a beta version" or "there are fewer animations" which just makes it clear that they have absolutely no idea what the hell they're talking about. I'm not exactly a top programmer, but I know enough about how computer games work to tell you right now, this stuff is garbage. It's not "a fact" at all.
What is POSSIBLE is that the game could become more sluggish and maybe slightly less responsive - nothing more than that - because of the strain of dealing with imported images, but this would only really make sense if the kits were a.) higher res than the in-game kits, or b.) in a different format. I'm pretty sure that b.) is not true, and I don't know about a.) (we've all noticed that imported kits look fuzzier in-game than native kits, and I dunno what's going on there). But the console loads the kits at the beginning of the game - I'm pretty sure it doesn't keep having to read them from the hard drive - so in theory even this shouldn't be a problem. And indeed, it doesn't seem to be a problem. For 99% of people.
If you want to play without the imported kits, and you're sure it makes a difference, that's cool. But most people disagree, so please don't go around insisting that this is a "fact" and acting like there must be something wrong with the rest of us.
It would probably also be nice if you didn't keep trying to hook more impressionable readers on this weird placebo, so they end up playing with crappy brown-and-orange striped Konami kits for the rest of their lives, telling themselves it's better this way. But I suppose that's their look-out. I'll stick with the nice kits, anyway, thanks.