Being able to buy class cubes was a feature we got SEVERAL years ago. Long before transplant passes. The fact you guys dont have it is unfortunate and feels like a gaffe.
That being said, considering the rate of how fast you can level up a new class once you get close enough to end game and the time period of which you have to cap on passes in a month is pretty generous. On top of that, efficient usage of passes requires at least 2 months of saving so there is no rush and general casual play will be fast enough to get what you need as long as your diligent.
I'm not saying grinding every day, but having a set schedule where you do the bare minimum most days of the week should be more than enough to make sure you pace yourself responsibility enough to get all the passes you need without fear of missing out. End gamer players get all 40 passes within 10 mins of the new cycle since we have a stockpile, but ya'll would be good too.
Explain please how you do your schedule?
Unfortunately, since I play primarily JP; I dont think you can copy my method. I don't play all the classes. All I do is do my weekly missions for my 2mil meseta per character and then spend 1.6mil to by 10 class cubes for classes I don't play. I end up spending between 3-5mil a month for all the class cubes I need, so when the cycle finishes, I instantly exchange my class cubes for passes and go about my day.
If you want a methodology for EN, then honestly, save up your keys, get your unplayed classes to 75 (do not unlock level cap), and do your featured quests for bonus keys and on your characters that have classes capped to 75, you overlevel for your cubes and keep them in storage. It's more efficient to do it on PSO2 Day for easier level as well. It's pretty hands off and doesnt require good gear or anything.