The hardware requirements that you found are correct.
There are multiple things to consider when thinking about hardware requirements.
Type Of The Node
The hardware requirements are aimed at Validators which participate in the consensus.
They need to execute time-critical calculations and can be slashed for not meeting the deadlines.
In order to have some baseline to calculating the deadlines, we opted for a reference hardware.
Ultimately this is only guideline and you can make your own choice.
Parity just provides these requirements as a reference, not a hard requirement.
Archive nodes and pruning nodes can basically use any hardware they see fit since they are not consensus relevant.
Custom indexer have to measure their own requirements.
Since most blocks are currently not full, you can probably use very cheap hardware.
Polkadot blocks are mostly not even close to their maximum possible weight.
Since the reference hardware is designed for 100% chain usage,
this translates to much less resource usage than to what is possible,
Regarding your concrete question:
Can OnFinality's nodes hit bottlenecks earlier than expected, due to their deviation from standard hardware?
Yes, it is possible that they would not keep up if the chain usage surges and they are using subpar hardware.
In this case its on them to make sure that this does not happen.