This is one of THOSE topics. Ask five different people and you will get ten different opinions...
In my humble opinion, though, how much tweaking is done -- and how much tweaking is desirable -- is very much a matter of what do you -- the artist (or in many cases, sadly, the producer, who may or may not be a philistine or a musician...) wants the final result to sound like. If what you want is the ultimate polished performance, not a mistake anywhere with every note precisely the volume and duration you want, etc. etc., then it is likely that good deal of tweaking and editing may be in store -- even to the extent of running the thing through a MIDI system, which is in the end a very fancy computer output with a rather complex input device and a complex program in there.
On the other hand, if what you are looking for is the feel and excitement of a live performance, then... there ain't no substitute for a live performance.
They both have their place.
If you should have the incredibly good fortune to have a very good high fidelity sound system, with a superb turntable, and access to a good clean copy (not played to death!) of some of the early Mercury Living Presence or London FFRR recordings, you can hear a completely untweaked, live performance in all its glory -- and there is nothing like it. Both of those series were recorded with a single (one!) very high quality microphone over, but slightly behind, the conductor, onto 15 or 30 inch per second single full track half inch reel to reel tapes, and then transcribed to disc without compression. Modern recordings may be slightly better technically -- but with those, you are there. The only experience which is better is a really good seat in a good concert hall.