Well not impossible to quantify - but impossible to quantify a meaningful SINGLE value that will be meaningful for different campaginsThere were also a lot of times where my fighter could attack from range while closing or target the enemy spell caster more easily. Things that are practically impossible to quantify on a spreadsheet. Ultimately, I had fun with the PC so it worked. YMMV.
If there's 1 turn per day that you can attack but another PC can't attack, we can quantify that impact. We can do the same for 2 turns etc. What we can't do is get a meaningful average number of rounds per day you can't attack because it's too sporadic and too campaign dependent etc. So those numbers can't be meaningfully calculated into DPR.
However, when looking at total accuracy weighted daily damage output they can at least be viewed there. You can then use that to calculate an adjusted DPR etc. It's the best way to handle such situations and not that much work on a spreadsheet. So in a way I can factor such a thing into a DPR style number - it's just you need multiple of them to show anything meaningful for different campaigns.