As a pro upright player I used an amp the vast majority of the time. When I first turned pro I used an amp for big band, but played acoustically for classical with a concert band. Eventually the concert band conductor suggested using the amp for classical as well. I reluctantly agreed to give it try. After the rehearsal he said he wanted me to continue using the amp, and over time I figured out how to make it sound a lot better. I have to say, the amp made playing in concert band much more enjoyable for me. However, I wouldn't consider using an amp in a symphony orchestra for classical repertoire.
Late in my career we had a big band leader who was really down on close mic'ing. He wanted the dynamics and tone of an acoustic ensemble. The audio tech adopted more of a distance mic technique. When I cross trained to audio, I experimented and (IMHO) improved on his approach. I used three AKG C414s on the saxes and a pair of RE20s on the bones. I also had a pair of mics on the trumpets, but usually the sax and bone mics picked up enough trumpet, so they were not on for section work. The horns mics were placed at a distance of about 4' from their respective sections. This approach definitely produces a more natural sound than having the mics stuffed down the bells, which I think sounds awful, but is very common.
This particular big band had soloist walk up front to take a ride. The solo mic was a C414 on a mic stand with a quick adjust clutch, so each player could place the mic at an appropriate height.
The mic was tilted down at about 45 degrees. This improved how well it picked up sax and took the edge off for trumpet. I spiked the floor with gaff tape to mark where the soloist should stand to keep the desired distance from the mic.
Distance mic'ing typically works well as long as the players don't expect a monitor. If a monitor is required, the mic has to be pretty close to the horn to get sufficient gain before feedback.
Eventually I was asked to mic the full concert band for indoor events. To my surprise I was often able to improve on the clarity, tone, and balance of a large acoustic ensemble without adding significantly to the volume.
Regarding dynamics. Flat dynamics somewhat correlate to using a PA, but IMHO a band can still have great dynamics even when they are mic'ed. I.E. correlation is not equivalent to causation. IMHO the responsibility for flat dynamics falls on the music direction and musicianship.
I don't have any sort of problem with people playing acoustically. IMHO, do whatever is best for the performance.