A 51% attack is when a malicious actor controls 51% of the network or more.
In most contexts it's a situation in which this person is double-spending coin and stealing.

Again, there is a very good reason why "another tube" does not exist.
It's because making another tube is not worth doing.
Because claims of centralization and corruption are in fact wildly exaggerated.

Anyone in the world can become a Hive whale at these prices.
There is no shortage of liquidity especially with futures markets in play.
The bridge remains thoroughly unburned.

But maybe you have a good example of a crypto network that's has a better track record than Hive.
For example: 1% of the Bitcoin wallets own 90% of the supply.
Is this a good target to shoot for?

If you want to claim that Hive is centralized then perhaps you could provide a target in which it is no longer centralized.
Or point to a single other network in this space that's doing a better job.