Earlier quoted context omitted.
Bitcoin Core removed that form of checkpointing, and added in another. Currently it has checkpointing in the form of assumevalid, which by default causes a full node to skip validation of transaction older than the checkpoint when synchronizing. [1] [1] https://bitcoin.stackexchange.com/questions/88652/does-assum...
Well, that is depressing to learn. So by default, a bitcoin full node DOESN't fully validate transaction history. If it finds a particular block at a particular height (that a group of developers have signed off on), then all signature validations in prior blocks are assumed to be successful. The reasoning is that you have to trust those developers anyway not to sign off on malicious source code.
As it is, tens of millions of people can easily stream 700 KB/s HD video 24/7, yet Bitcoin is being kept to a throughput of 2 KB/s based on the claim that increasing it to satisfy market demand would lead to Bitcoin becoming centralized, with only large corporate entities left being able to fully validate.
It's pure FUD.