What if some attacker forks blockchain from height 1 with a constant difficulty 1? I've been reading Satoshi's paper recently. There's one thing I cannot think through.

That is because the target will limit the block production speed to 2016 blocks per two weeks on average no matter how high the hashrate gets. What if the attacker forks the blockchain from height 1 with a constant difficulty 1 and produces exactly 2016 blocks per two weeks (just in timestamps, not in real time). I think it will be very easy with such low difficulty to catch up current blockchain's length, and eventually surpass. According to the longest blockchain concensus, will the fake blockchain replace the current one?

I would be grateful if someone could clear up my confusion.
The accepted blockchain is the one with the most cumulative difficulty (i.e. the one which requires the most work to produce), not the longest. Nodes will not even accept a chain which has less than some minimum work required, set in the code, to stop such an attack from happening on newly synchronizing nodes who are not aware of the main chain.