first of all you can not eliminate manipulation so it will always exist. and based on my experience even without manipulation the "highs" would have still be near the same thing meaning I believe it would have been nearly $20k because it was the FOMO with a little bit of manipulation that pushed the price up there. and it is always easier for bitcoin to go above certain levels when a big resistance like $10k is broken and you enter uncharted waters.
drop on the other hand is much harder and needs a lot more manipulation than the rise because people tend to have bull mentality when it comes to bitcoin even if they pretend otherwise so making them sell is harder.
What experience do you speak of where you say it was barely any different to how it would've been with it. I think that you're right though. Manipulation will always exist but to what extent it makes a difference is really impossible to know.