The way you have approached this matter would suggest to me that you are regular air traveller. Albeit, usually with a half decent scheduled operator. So when you travel on your cheap package holiday, you should appreciate that the charterers are not charging the high prices that a scheduled carrier charges.
If you are not a regular traveller, then here is a quite simple explanation as to why MYT would have 10 abreast, as opposed to 8/9.
1) You have paid peanuts for a holiday
2) Only a percentage of the total holiday price goes to the charter airline
3) Charter airlines don't sell seats at different prices. Each one is the same, as oppossed to first, club, fully flexible, restricited tickets, etc......
To ensure the charter airlines make money they have to have greater utilisation of their main asset, than that of a schedule airline. Again due to the fact that the fares they charge are a damn sight cheaper than that of a schedule, and as a result, so is the standard of comfort. Unless you are a midget, you will be uncomfortable.
So, whats the answer. Use a schedule airline for any flight over 2-2.5hrs in duration. And also expect longer delays than a schedule carrier, because they just don't have the downtime built into their schedules.