firstly if your a malicious pool with lots of hashpower you own to match/beat honest network of pools and miners.. or even if you collude or intice many individuals to collude with you to get hash power.
even if you reversed old confirmed transactions. YOU can only then respend the transactions no longer confirmed if you own the private keys to the funds of the transactions that you edited out of the blockchain that you re-orged.. you cant just steal other peoples transaction value. you can only make their transaction no longer exist by going back. this means its only financially viable to do block re-orgs if YOUR transactions you signed previously and got confirmed to spend with a service, got reversed for you to then spend that amount again..
but you would only be able to do this effectively if you when spending first, received goods or services or another curency to keep that value. to then reverse the transaction to then spend the transaction amount again to double your value.

this means spending alot first, waiting for the service to accept the amount is settled, release their goods/service/other currency to you, wait for you to deem that other value type as received and then edit the blockchain to double spend the initial transaction amount you then edited out the blockchain

this means after receiving the goods/services/other currency, then going back to edit the blockchain
this means having to go back several blocks to edit the block containing the transaction you made of significant value to be worthy of reversing. and then catch up with the honest networks list of blocks and over take it.

this is not something you can do within just a couple blocks of the honest network.

by honest users receiving significant value waiting 6 confirms to treat it as settled and release goods. you are looking to need to go backwards a minimum of 6blocks meaning honest network then gets a blockheight headstart of 7 blocks ahead of dishonest pool, which then have to build on to catch up
this 7 block difference takes time for the dishonest pool to catch up
(reality is if an exchange service does fiat withdrawal from your initial btc deposit you are not only waiting 6 confirms for the deposited to be acccepted but then waiting for X time(can be 72hours(432 blocks)) for the fiat to clear your bank on withdrawal request)
(reality is if you buy goods with your initial btc spend, you have to wait for delivery of goods which would be alteast next day(144blocks))

so for you to then go back and then undo- your confirmed deposit/goods spend tx.. you then need to catch up

now lets again ask you to do the math
a 51% of honest network(2% advantage) is not enough to race against the honest network that is minimum 6confirm but more likely 150-438 blocks ahead..
work out using math how many blocks it would take before the dishonest network can overtake the honest network

hint if just 6 confirm lead. the dishonest network with a 10% advantage(55%) would need atleast ~44 blocks just to re-org a block that was initially just 6 blocks behind when the attack was initiated* and would need over 55 to be then 1 block ahead of the honest network

the more blocks a malicious pool need to go back. the more speed blocks it would require to build on from its edited block to then catch up

*


what you also find out is during those missing time blocks of dishonest catch-up time. there may be some miners working on that pool seeing that although it aided in building 40+ blocks for its pool for the pool manager to double spend pool managers funds. the miners are not seeing the proported block has and previous block hash of its attempts visibly on the honest network yet, thus think they are running on some altcoin, so they would to protect their investment, would jump to a honest pool whos blocks are visible

again the dishonest pool wont show results instantly. but would take time to get ahead to have results seen and the more blocks it has to go back the longer it takes to catch up to show results

run the math

---

as a separate argument about the effect of the malicious pool having on the market price
if a malicious pool were to be winning blocks half of the blocks where the honest pools have competition.. the cost of mining for the honest side doubles as they would only be winning half as many blocks compared to pre-attack. thus they wont want to sell at a loss and so the market speculation would be like the hashrate has doubled which is like a halving of rewards per miner competing. and so the market would actually want to go up as less would be willing to sell for less

even the dishonest miners will want to recoup ROI from their investments and not sell rewards at a loss and so they too wont want to crash the market and due to the competition on the hashrate causing mining costs to double for te network as a whole, they too wont sell cheap but instead push the market up