It would not be rejected because we assume that the malicious branch is valid and nodes would have all of its blocks. So the incoming malicious block would have a previous hash that matches a block in the malicious branch. When the malicious branch becomes longest, there is a reorg.

A malicious block would be accepted because its previous hash matches a block in the malicious branch. Their are no invalid blocks so none are rejected.

In order for honest nodes to reject the malicious branch, which we assume is the longest valid chain, the consensus rules would have to be changed so that a block in the malicious branch becomes invalid. That would require all honest node operators to install a new version of the software with the new rules. The attacker doesn't have to incentivize anyone. As long as the attacker continues to make the longest valid chain with its majority hash power, honest nodes will follow it.

you obviously didnt read.. if the prev hash doesnt match then its not part of the chain (hint: 'orphan'(unknown parent))
also look into how altcoins fork off, it doesnt require the genuine honest network needing to change. its just where there is a mismatch of chain of hashes, for a new lineage to proposer the new lineage has to do things to continue building on and not reject(by banning the honest pools/nodes broadcasts)

so without a army of nodes on the malicious pools side the malicious pool has to do some extra things to not only produce blocks but also try to get its ancestry of differing 'previous hash' to be accepted by honest nodes without ending up rejected and treated as a solo pool altcoin with no community

there is more to block acceptance than just your theory of valid transactions.. such as the changetip work whereby to also try to win the height competition the malicious pool would need more than equal power to be able to do more work in less time to show a higher 'proof work', difficulty to be accepted as the more worked on chain, because the 51% is more of a minimum not a target. because anything below 51% would probably be working on a lower difficulty to create fast blocks and just rejected based on less proof work or would not be solving as many blocks so never overtake the honest network in height or difficulty

That's why Bitcoin block time is set to 10 minutes, not seconds. And also: if you have a coin, where "uncle block" is a valid thing, then it is a completely different situation. Ethereum simply lowered their block time, without understanding the consequences.

Many coin creators decreased their block time from the default 10 minutes, but when I tried to build my network, I did the opposite, and actually increased it (for example into one hour, one day, or even two weeks). For example: if you want to have decentralized DNS, then you don't really need to update your naming indexes every 10 minutes. Establishing a domain is a long process, so you are not in a hurry, even in the centralized model, so there is no reason for giving for example 50 new names every 10 minutes, you can do that every hour, or every day, and that system would be better.

First, many altcoins rejected double SHA-256, and tried something else. And then, suddenly, they were protected from attacks from Bitcoin miners, but at the same time, they opened their network for the new attacks, from the new, unexplored hashing algorithms. And then, they are suddenly surprised, that they don't have the largest base of miners on their side.

Just use Merged Mining properly, and it can deal with those things, if you manage to calculate the global difficulty correctly (not like NameCoin, which only counts their own difficulty, without considering global hashrate). Collect all valid headers, to compute the real global chainwork, even without collecting block data from altcoins (just headers are enough).

As far as I know, no chain did that properly, not even Bitcoin. Because BTC is safe, when forks have something like 1% of double SHA-256 global hashrate. But it won't be safe, if you are on that "1% side". However, it could be fixed, and I wonder, why no altcoin implemented those kinds of protections, and instead, they are all blindly calculating only their own difficulty. It is like closing your eyes, and pretending that BTC doesn't exist, if you still allow mining a new block, for providing 1% of the global hashrate.