I wasn't directly referring to "volume" output, rather the "pitch" as played.
I surmise that the current tuning is A(something, maybe "4") is still 440 Hz (but it may be upwards of 450 nowadays). I've got some recordings (with either actual "period instruments" or faithful reproductions) where that "A" is much closer to 400 Hz, as was the custom before steel strings and greater (violin family) neck angles were introduced to attain greater volume (I have it on fairly good authority that even most "Stradivarius" instruments still in use have been thusly modified!). Then there's the (keyboard) tunings which didn't follow a strictly "mathematical" scheme until very much more recently. "Perfect pitch" really doesn't mean anything in the big picture.
It's humorous to hear Mozart's works played on modern instruments in a modern fashion. Well, actually, it's not funny; it's quite sad. Not to say he wouldn't write music appropriately for them if that's what he'd had available, but he didn't, so he didn't. A lot of the finer details in his music get lost on a regular basis nowadays. Fiddle players (and others) usually now play with such a heavy, constant vibrato as a matter of course (Mozart was a virtuoso violin player, and letters between him and his dad mention players already flirting with that then, described in the letters as if they'd had a "palsy"), that many of the finer "turns" in his music get totally lost when played that way. I humor myself with the notion that when played, the musicians likely give each other a funny wink as if "why did he write it that way when you can't even hear it!"