Blockchains come in many forms, the ones you are thinking of are what are called Proof of Work chains, these uses a kind of cryptographic race to secure thier data and use a TON of waste energy as a result. Def not a fan either.

The growing popularity and interest in chains is around forms of Proof Of Stake, these use other internal protocol mechanisms to secure the network and work to run the cryptographic functions as efficiently as possible. Unsurprisingly the fastest blockchains are proof of stake and power wise are similar to traditional applications in utilization.

You don’t need any of these networks if you don’t want to use them, fundamentally, they arent even networks, they are cryptographic messaging systems. How the data is sent and processed is incidental, you could work out a bitcoin block on pen and paper if you wanted. This concept has extended to a cryptographic tool called Zero Knowledge Proofs, these will be part of next generation identity verification systems and is a fundamental of the W3C standard around DiD, the whole point is for disconnected attestation.