No, Not all Blockchain apply slashing but many blockchains using proof-of-stake (PoS) and delegated proof-of-stake (DPoS) consensus mechanisms, uses slashing to punish offenders, or account owners especially Witness that breaks rules and regulations of the blockchain.

I agree with you that blockchains that I working on I am mechanism of proof of stakes only are using the slashing mechanism for giving punishment to their validators of their misconduct but if we see on opposite side and we talk about other blockchains like steem then they are not using flashing mechanism for giving punishment to their validators as they are working in delegated proof of stake mechanism.

Slashing is a very powerful but new technique that are used in fewer Blockchain, so therefore only few developers can understand and implement it successful and easily. Implementing the slashing punishment technique can be very very complex to handle.

I totally agree with you that slashing is very complex mechanism because you have to be attentive while making any decision but our you presented a good article with us and I wish you success in this engagement challenge in which you tried your best all the questions as required.