For indoors use IMO it's a complete non-issue, unless you happen to have your desk right where the sun hits your laptop at some point during the day.
For outdoors use I wouldn't compare MacBooks to recent Windows laptops, particularly touch enabled ones, as the latter tend to have significantly glossier and more reflective displays than the MBs.
If you intend to use your laptop for graphical / visual work it's also a non-issue as you shouldn't be doing it at 350 nits anyway (well unless you're working on HDR content and absolute brightness values that is) and absolutely not with the sun shining on your display.
As far as I'm concerned, as a photographer, the big question is whether the MBP' extra brightness simply is 1) a software switch, or 2) a question of selection during the manufacturing process after calibration / sample variation evaluation, or 3) a real, tangible hardware difference, and what each of these mean in terms of other differences regarding display quality (evenness of the white / black points and colour temperature, max contrast, etc.).
I really hope that it's 1) in which case I'll be able to save an extra €320
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