You appear to have a very specific idea of what a WC is which is simply based on how the IM WC have been run until 2019. It doesn't reflect how WC are organised in most sports (or even in non-Ironman triathlon), especially if we are talking about Age group / Masters.

I won't go into details of how those WC are run (many events don't even have a qualifying standard - whereas to get a Nice WC slot even considering rolldown you should have at least completed an IM in the previous year, which is already a qualifying standard and more than other sports).

Anyhow at the end of the day it really doesn't matter how many people attend (do you imply that the 70AG title is less important than the 50 because there's less people?) and how they were selected (if we look within and outside of our sport there's enough models to discuss this forever) as long as whoever is interested in the WC AG title offered by the organisation (Ironman in this case) is there.

Even the comment of the watering down of the race that often gets thrown out has no impact on the race at the front. Also, it's very easy to demonstrate that a higher participation increases the competitiveness of the race because any selection method will exclude competitive athletes (one of many examples: some of the best teams in soccer world cup are excluded by the qualification system pretty much every time).

It may be your idea to run WC a certain way and to value the race based on a specific slot allocation formula and it's ok for you to have this idea, just don't expect everybody to necessarily share that same idea. There isn't a single absolute way to run an AG WC.