The numbers are irrelevant. It's just an arbitary scale.
If you were experiencing a pain that's so mild it's basically just a feeling of discomfort, you'd be able to describe that, right? And you it you were experiencing a pain so intense that it has you literally screaming? You'd be able to describe the difference between them, right? Well there's literally a conversion chart that translates those feelings into numbers.
You don't have to conceptualise anything — it's literally printed on a paper for you when they ask you the question. As long as you can experience pain and either read a description of pain severity, or describe your pain severity to someone who can read, you can use a numerical pain scale.
Literally the entire point of the comment that you're responding to is that it isn't true for the metre, and it isn't true for any SI units.
Your entire claim of tautology rests on the assertion that the speed of light is defined by something external to light itself. That's false. It remains false irrespective of which SI measurements you swap in.
Just because the speed of light can be expressed in terms of SI units, doesn't mean its definition depends on them. Which is the point that wolframhydroxide was making.
This directly disproves your original assertion of tautology.