In 2018 when the bitcoin network hashrate first broke 25 EH/s, a 51% attack required another 25 EH/s. But where would another 25 EH/s be found? There wasn't another 25 EH/s of hashrate available from the manufacturers (as far as was known publicly), so other than collusion among the existing miners of at least half the hashrate (~12.5 EH/s) there was little risk of a surprise 51% attack occurring.

We just had a drop in hashrate, and will likely see further drops as more miners power down (awaiting better conditions), and we are likely to see further bankruptcies and liquidations occur.

Most of that hardware still has some fair amount of value, just not to the existing miner who could use it to mine profitably. So that hashrate capacity may not be online, but it will eventually return. Other models of equipment are so obsolete they are being decommissioned and warehoused. Some devices are being discarded as e-waste (generally because they would require repair), but even most 2017-era S9 rigs are still mining -- thanks to them being repurposed as "space heaters", or for other specific use cases (e.g., only run when negative rates occur, such as when wind power is in excess of demand).

So consider if this were to continue ... where the estimated hashrate were to drop to let's say 150 EH/s (almost just half of today's level), but that level of hashrate is coming from 300 EH/s of capacity that exists and is functional, but just not running 24/7, or runs seasonal, or is offline in reserve with the expectation when profitability returns they will return to service.

In that scenario we still have the question of ... where does this attacker find an extra 150 EH/s of hashrate in order to perform this surprise 51% attack. And could this attacker even amass 150 EH/s of hashrate without suspicions as to intent be raised (as in, why did they build the farms to run the hashrate but not mining)?

But to directly answer your question of "Would 1/100th be easier to 51% attack?" Yes, if in a short period of time the hashrate were to drop to 2.5 EH/s, it would be not hard for a miner to acquire and secretly run 2.5 EH/s and perform this 51% attack. I can't imagine too many paths that would result in hashrate dropping to 2.5 EH/s barring nuclear attack, EMP, meteorite, etc., ... so in a scenario where one of those occurs, bitcoin mining being at risk of a 51% attack becomes the absolute least of my concerns.

Now let's even assume that hypothetical where, at a drop in hashrate to 150 EH/s, an attacker has amassed another 150 EH/s and is ready to perform the attack. What is their aim? Remember, a 51% attack lets the attacker do two things: 1.) censor some or all transactions, ... or 2.) mine a private fork so as to have the attacker's public transactions confirm, then at a later time release the private fork which results in a blockchain reorg that invalidates the earlier transactions that have "confirmed".

So what does the attacker want to accomplish? They can start their private fork, deposit coins to exchanges, then withdraw different coins, then when those withdrawals have confirmed they can reveal the attack (i.e., invalidate the earlier deposits). So those exchanges attacked are immediately insolvent. Is that bad? Yes, for those exchanges and for those who had funds at those exchanges. Is it fatal for bitcoin? No. No it's not. Just like 3AC, Celsius, and FTX fraud wasn't fatal for bitcoin. And there are measures that can be taken to reduce or essentially eliminate the likelihood of a similar attack in the future.

And the final argument is ... but what about a nation state attack (versus the attacker's motivation to achieve profit)? Bitcoin mining is a protocol, currently SHA-256. The bitcoin mining protocol could be changed, and with that change the nation state would have spent billions of dollars for ASICs, transformers, mining farms, staff, etc. that no longer are used because the protocol for bitcoin was changed to something that doesn't use them SHA-256 anymore.

tl;dr: bitcoin mining is resilient against the threat of a 51% on the way down, just as it is on the way up.