Assumptions should not be the basis of any decision
Self evidently.
If you are unable to form a sufficiently accurate assessment of the runway state; ‘if you don’t know then don’t go’.
In the ideal world, yes.
The real world is rarely ideal.
Using PIREPS is an assumption; that those people have a better understanding than you, but what is the basis of their judgement.
A pilot who has just landed on a waterlogged runway has a better understanding of the runway condition than a pilot waiting to take-off.
Safety related decisions should not be delegated either by assumption or using reports of unknown quality without compelling evidence and consideration.
In the example I mentioned, I approached the holding point of the TO runway with a crosswind that was
either just within,
or significantly outside of the crosswind limit,
depending on braking action (which was not available from ATC).
As I waited I watched a BA B787 in the latter stage of his approach. In the extremely gusty and turbulent conditions I could see him struggling to control the aircraft - and he did a damn fine job, putting it down in the TDZ and braking to clear the runway.
When he was clear I asked him for a PIREP. He replied 'Medium' and that put our take-off out of limits.
There are some airlines I might hesitate to put credence in for PIREPS, but BA is not in the habit of putting aircraft off the end of runways, so I definitely heeded that PIREP. And of course it confirmed what I suspected - less than good braking action, and a no-go.
Conditions can change quickly in tropical storms, bands of rain sweep through bringing worse weather, and then they pass, giving temporary lulls. In addition the eye of the storm is moving, so the bigger weather pattern is affecting wind direction over time. I anticipated the crosswind would begin to reduce after a while. So we waited. We did not 'give up' and decide to 'not go' because the company I worked for (an Asian airline) would not support any such decision. They would expect me to provide EVIDENCE that the braking action was not GOOD. Giving my 'opinion' would not cut it.
This is where your 'ideal world solution' clashes with the real world for many pilots.
By the way as we sat and waited for things to change (about 45 minutes - I took the extra fuel expecting this to happen) we saw around 10 aircraft take off. Including same type aircraft. Pretty tough to sit there and wait it out while everyone else is just blasting off. But in the absence of airport measured braking action reports they may well have all felt entitled to do so!
Would you have been one of them? Because the consequence of your choice to ignore PIREPs is to put ALL your decision making on your own judgement - which (as you point out) could be very wrong. And if your answer is always 'then don't go' I don't think you'd have a job for long in these here parts.
The wind subsequently backed onto the runway sufficiently for us to depart in a lull.
I still feel I did the right thing by my passengers and crew in obtaining that PIREP, and delaying the take-off.