I am late 40s. I had a few fillings in my childhood, but I'm not sure they were unnecessary, because my sister, two years younger, didn't have any, which seemed unfair, as she was the one who added sugar to breakfast cereal and so on, not me. (She has since had a root canal and stuff, so it's balanced out a bit.)
My last two fillings were when I was in the 6th form, and he did white ones, which were new, "but the NHS is paying for this." He had quite strong views on the importance of the NHS and dental health.
Mum and the two of us went for check-ups every 6 months. We kept the same dentist from cutting our first teeth until he retired about a decade ago. Our water wasn't flouridised because we weren't on mains (foarm with a borehole.) But it was a very hard water area (through solid chalk, basically,) and the dentist had some theory about calcium carbonate (limescale) in the water and levels of plaque, though I don't remember the details.
We also had the school dentist, and I remember giving out free disclosing tablets, and we did use them. I don't remember anyone using toothfloss unless they actually had something stuck in their teeth - it wasn't something you did regularly.
I had an extraction either side on my top teeth, as I had very crowded teeth, and now have small gaps, but not enough gap for a whole tooth. My bottom teeth are pretty crowded and a bit uneven as a result, which I suspect may start to cause issues in the future.
Although some people may have suffered unnecessary extractions, I don't think it was a universal practice. I think that the NHS meant many people saw the dentist who otherwise wouldn't have, and still does, even though it can be hard to find an NHS dentist these days. I think there have been changes in dental practice - I now routinely get my teeth x-rayed as part of a check-up. I don't think that was available at all before my teens (so mid-'80s or so,) and at first was on for investigating possible orthodontic work or problems rather than being routine. Though it may just be that it's coincidental timing with me having adult teeth and getting a retainer. But I remember a dentist friend of my parents in another part of the country being excited about the new x-ray machine they got in the practice, and that was mid-'80s. I don't think people talked about seeing the hygienist then, either, whereas that's now routine. And although electric toothbrushes were available in my childhood, they're much more commonly used now, and mine has a timer and stuff, and you can get different heads. Even manual toothbrushes, in the '70s, the only real difference was closing your colour. Now you get different hardnesses of bristle, there might be plastic bits to massage the gums, and fancy stuff like that.
So a lot of problems will be picked up before a filling or removal is necessary, and brush technology and practice means we probably have better hygiene- pretty sure I do, anyway. But there are still those who don't go to the dentist, and don't have good toothbrushes techniques, if they brush at all, so while there are fewer fillings and lost teeth these days, there are also those bucking the trend.