Fine, overall skill has increased. But given the vast amount of information and strategy guides, it is much easier to get to a diamond level now than it was before.
That idea doesn't seem coherent to me -- Diamond is just another way to say "top 60-90th percentile". The vast amount of information is available to everyone equally, so it doesn't explain why some people are above average players. Players in every league have improved.
There's no static "diamond level" way of playing that's been unchanged over ten years to compare against.