Ultimately I'm skeptical of price manipulation theories that rely on executing big trades to artificially move the price, as opposed to moving the price via changing trader sentiment about the underlying asset.
There is a chance trader sentiment latches onto a price change and you start a herd movement just by making a big trade, but I think it's a LOT harder to pull off than it sounds.

My gut feeling here comes from another environment, PredictIt betting markets, where both the number of traders and the size of the investments are capped so the markets are smaller.
The order books there are also directly visible, so you can calculate how much it will cost to move a market price by a given amount.
There are many markets on there with order books thin enough that a hundred bucks will move the price by several percent.
You can experiment with this manipulation on a middle-class salary there, and you'll find that unless you accompany your price swing with a compelling pump story in the (unregulated of course) message board, it doesn't last long enough for you to get out.
Some of the really small-cap cryptos might be another example of a playground to try stuff like that out in.

I think most traders in both short and long positions are not attempting manipulation, and just expecting that the market will naturally move to a more realistic (in their view) valuation of the stock.

Here are the mirror scenarios as I see them. The price-moving influence for a given capital investment is no different between the short-seller and the long-buyer.
And in both, it cuts both ways -- the trades you make exiting your position have a market force opposite to the trades you made creating it.
There's no free lunch. Winning either trade requires convincing other traders that the higher or lower price is a fair one.
That could be done with false info if you're a scammer, or it could be real info if you are just trying to make some money off pointing out the truth (see Nikola).

Scenario A:

I am a short-seller. I borrow $100M worth of stock from a broker, and sell it with a market order.

My sells chew through the bids on the order book, highest bid first, moving the last share price number down as I fill the standing orders of everybody buying at X, then at X-1, then at X-2, etc.
But I haven't affected the ask side of the order book directly. Those people are all still offering high prices to sell, I just jumped the line ahead of them and told all the buyers "I'll beat that price! Get your cheap shares here!".

I hope that some of the people on the ask side see the movement, panic and either execute market sells or at least lower their sell limits, so that I can buy the shares back cheap.
But they might not, and if they don't, I'll have to buy back higher than I sold. I really need for this to catch on and cause a frenzy, because in moving the market down I sold a lot of my shares at bargain prices!
To make money on those I'll need the price to sink even deeper so I can buy them back at extra-bargain prices.
In trying to keep the price low as I repurchase shares, I'm fighting against other smart traders who see that none of the fundamentals have changed, do not wish to sell low, and may even be competing with me to buy low.
I'm also fighting against myself in a way, because just as I put downwards pressure on the price by selling this huge number of shares, I'm now putting upwards pressure on the price by trying to buy them back.

Scenario B:

I am a buyer. I borrow cash to buy $100M worth of stock with a market order. (You may ask who would lend me that much cash, but in scenario A they don't lend $100M of stock to just anybody either so we're comparing apples to apples)

My buys chew through the asks on the order book, lowest ask first, moving the last share price number up as I fill the standing orders of everybody selling at X, then at X+1, then at X+2, etc.
But I haven't affected the bid side of the order book directly. Those people are all still offering to buy at low prices, I just jumped the line ahead of them and told all the sellers "I don't mind your price, I'll take all you got!".

I hope that some of the people on the bid side see the movement and think, this rocket is taking off! Hopefully they either execute market buys or at least raise their bid limits so I can sell them shares at the inflated price.
But they might not, and if they don't, I'll have to sell lower than I bought. I really need for this to catch on and cause a frenzy, because in moving the market up I bought a lot of my shares at highway robbery prices!
To make money on those I'll need the price to rise even higher so I can sell those shares at extra-highway-robbery prices.
In trying to keep the price high as I dump my position, I'm fighting against other smart traders who see that none of the fundamentals have changed, do not wish to buy high, and may even be competing with me to sell high.
I'm also fighting against myself in a way, because just as I put upwards pressure on the price by buying this huge number of shares, I'm now putting downwards pressure on the price by trying to unload them.