Oh, and I suppose "stealing" rating points sounds a little silly, or weird.
What I mean is... anyone who gains rating points is, in the eyes of the system, underrated (that's why their rating is adjusted upwards).
So in this sense injecting players who become better than average is the same as injecting underrated players, and it's easy to imagine the effect of a lot of new underrated players... as they play us they steal all our points!
Since there are a lot of effects (most I'm sure I don't even know about) pulling both ways (inflation and deflation) I'm not saying this is the whole picture. But because I believe players are better today, on average, than 50 years ago, I'm making the argument that the influx of players cannot have had an inflationary effect.
The puramid example is absolutely correct and it is a surprise that so many people don't understand it.
I think it's the opposite
I think it's so simple to understand that people don't take the time to think it through.
Let's assume a chessclub has 10 players 1200. If they play ony aginst each other then only 3 will go over 1300 ,none over 1400(even if he does he will have to beat all of them continously for a decade). If they are all 1200 strength, then they will all remain 1200. Sure some days will be good or bad for individuals, but if they are 1200, then on average they will all remain 1200. This is the first flaw of the pyramid example: it assumes no 2 players can be rated the same rating. The other mistake is it's not actually a pyramid shape to begin with. It's a bell curve, so if anything, it's two pyramids stuck together (one pointing up, the other down). I will agree though that bringing a large percentage of the general population into chess would make the rare skill levels (at both ends of the bell curve) more common. But again, rare skills aren't necessarily rare ratings (more on that below).
If on the other hand the same chessclub has 100 players rated 1200 then more than 30 will go over 1300 , more than 10 over 1400 and at least 1 over 1500. It's common sense! Since ratings and skills are different, instead of that example lets imagine 100 players in a club where the ratings are 1000 to 2000 and the average rating is 1500, then 10 newbies join. All 10 later become rated 1900-2100. To do this they had to win a lot against everyone else. As a consequence, the average rating of the club went down, and the new top players are, of course, better than the old (otherwise they wouldn't have replaced them at the top). Anyway, this is the basic idea, it depends on whether the players you're injecting become better than average and remain active. There should be many inflationary and deflationare (if that's a word) effects, but as for the effect of the next generation, this would be the general idea: injecting a lot of new players who win a lot are in a sense "stealing" rating points
Amateur players are worst than they were. The abundance of resourses matters for good players because they know how to use them but it leads to confusement and misuse for all the rest. There is a big number of amateurs that are trying to learn from engines and databases and they never learn anything. The books that were good 40 years ago are good today too. The methods that were good 40 years ago apply today too. The main way of developing skills hasn't changed even a bit. Some things have been improved, some good books have been added but the bad books are so many more(more than 9 out of 10 new books are average or below average). Today is harder than ever to pick the right training method or the right book or the right coach.
You make some good points here, but I"m not totally convinced. Sure the new player will be hit with information overload, but moving past the beginner stage, I think they still have it better. I can get unlimited tactics for free, GM instructional videos for free, and play opponents 24 hours a day, 7 days a week for free.
The only resources that really matter for a player are 2 : A good chess club(not obligatory but it helps) , access to an abundance of good open tournaments(absolutely mandatory) and good choices(picking the right way to study or the right book to read is certainly very important).
If you have these 3 , resources can help you , if you don't , not even God can help you.
For the players who become very good, I'd add a database is important. Years ago people luged around reference books and files from tournament to tournament. These days you can have a million games on your laptop. Learning from past masters has never been easier, and e.g. chessgames.com is another free resource.