That's a gross oversimplification.

For a start, there are many different ET fares and generally 4 different CE fares. So for each of the multitude of Euroland fares, you are buying:

1) a different cabin (product)
2) a different level of flexibility/ refundability/changeability
3) a different inventory, so more/less shortageofseatness
4) with more/less advance notice, so more/less lastminuteness
5) and having to pay different taxes based on cabin, so more/less taxiness

While the cheapest O or G class may be 2-3 times cheaper than the cheapest R class AFTER tax (notwithstanding the fact that O class is generally changeble/upgradeable for a fee, while R class is a weekend use-it-or-lose it fare), the difference BEFORE tax may be FIFTY times.

G class to AMS is £4 return +tax (eat that, Stellios), while R class is £227+tax.

Meanwhile full Y class may be more than many of the CE fares (even some flexible CE fares).