"So-called bitcoin miners expend tremendous amounts of computing power to verify transactions and link them"
If this is true, shouldn't the ability to mine be limited by the computational resources needed to perform these tasks? Instead, it seems people increase computing power with no apparent limit in order to mine, and the "demand" for that power is never met.
Bitcoin's security relies on the true blockchain having more Proof of Work in it than any attacker could create. A Proof of Work value is a proof that you had a computer spend about a certain amount of processing time tied to a specific input value. Someone with one computer can't produce Proof of Works as fast as someone with multiple comparable computers. Someone trying to take-back a Bitcoin transaction and create an alternate blockchain with their transaction removed can't create Proof of Works as fast all of the world's Bitcoin miners working together (unless they have a secret god-tier supercomputer, or somehow convinced most of the world's existing Bitcoin miners to work for them instead).
What matters to an individual is their percentage of the overall mining power, not their computing power in absolute terms.