Brushing teeth is a must but flossing wasn't proven to have measurable effect on teeth health last time I checked.
I’ve worked alongside dentists in and off in a marketing capacity. I’ve also been married to one for 15+ years and I can tell you that every dentist in the country can look in your mouth and knows whether you floss regularly or not by the amount of plaque built up between your teeth. And plaque is bad. The NIH published an article shortly after the one I mentioned above to try and combat the misinformation: https://newsinhealth.nih.gov/2016/11/dont-toss-floss
More on Snopes: https://www.google.com/amp/s/www.snopes.com/news/2016/08/06/...
TL;DR: flossing is poorly executed by most people (much like brushing) and the studies on it are flawed, but you’d be hard pressed to find an oral healthcare pro that would recommend against it, and almost all are for it. And no, there is no “big flossing lobby” pushing it.
https://en.wikipedia.org/wiki/Dental_plaque
Here's a study (just read the summary here) that says a water jet (waterpik brand,) is effective. No idea who paid for the study and didn't research the plaque types mentioned against the wikipedia plaque article to see if there are other types of plaque.
https://www.ncbi.nlm.nih.gov/pubmed/19385349
I have to say if I go a couple days without flossing (once in the evening,) but with water jetting, I can feel the floss sliding across something, presumably the plaque/biofilm between the teeth before the floss cuts into that layer and I can feel it against the tooth. I use one of those forked flossers which isn't the best approach as it doesn't wrap around the tooth but you can pivot the fork to get some extra coverage. It makes an onerous task slightly less onerous.
You can buy plaque staining tablets to visually evaluate your plaque condition. Buy some, water jet and test. Floss and test. let us know the results.
I do both plus an Oral-B electric brush. Probably too much for most people.
EDIT: Also, we understand the mechanism by which food left in the teeth contributes to gum disease very well. I'm all for demanding high quality epidemiological evidence when we just have a hunch about things, because we deserve at least some correlational power to any claim, but the way in which this data is collected by something as difficult to monitor, annoying to some people, and socially pressured as oral hygiene is deservedly suspect IMHO given our direct clinical knowledge of the health matter in question: it's aetiology, progression, and reversal, on an observable level per organism is very well understood by modern dentistry, AFAIK.
Strangely, I've had one dentist tell me Glide floss is horrible and I should use some other floss that's "fluffy" (sorry, can't remember the brand/type, I think it was a J&J product), while more recent dentists give me Glide samples every time I visit. I tried that other dentist's recommended floss for a little while, but it was the absolute worst I tried in terms of tearing; it was basically unusable because it just kept getting ripped in half due to my tight contacts.
There are lots of mechanisms your body has that are adequate enough to get you to puberty, so you can reproduce.
If you want better than adequate, you should floss.
Prehistoric people did live to old age if they didn't get killed by disease or wild animals or accidents or murder, but they probably didn't look too good at that age and probably didn't have many teeth left either.