The nature of Proof of Work is in a way that 51% attack is a real attack vector but it depends on a big "if". IF one entity can gain control of such a large hashrate they can theoretically carry out such an attack.
2 more things, you can't really compare any altcoins with bitcoin.
Also this already happened a long time ago in bitcoin as well. The mining pool was called GHash.io back in 2014 and it briefly gained more than 50% of the total hashrate (for real) and nothing was halted and nothing broke. The miners left that pool (switched to other pools) and its hashrate came down.
Two big ifs are like
No entity owns enough dominant hashrates to do 51% attack on the network.
Another bigger if is, when an entity has that dominating hashrate and is able to do 51% attack on the network, will that entity do this?
The answer is clear.
After spending a lot of money for owning such dominating hashrate that can help to mine many Bitcoin blocks (in this example about Bitcoin blockchain and 51% attack on it), and get very good revenue for the mining business, why that entity need to attack the network with very unavoidable high risk that Bitcoin price will crash?
There is no need like this, and intelligent Bitcoin miners will never do this.
There were times with dominating mining pools like this but they did not make 51% attack and they surely had big reasons.
https://hal.archives-ouvertes.fr/hal-03610424/documenthttps://petra.isenberg.cc/publications/papers/Tovanich_2020_VAO.pdf