You are absolutely right. I was on the same boat as you, and since Custom Fields were developed, ASANA became a game changer for how projects are managed. You can make this feature do wonders (or so I believe )
There are several ways you can highlight the priority of the tasks within a project to get it appearing within the filtering of All Tasks.
It all depends on the user case you have. I will give you couple of options for you to go through and hopefully they will answer your concerns:
You can add a custom field for task priority. Make the custom field drop down menu and choose the priorities you and your team work with. Once that is done, you can go to the view options of the project and select to view them in the priority order you have. Save that viewing option for everyone and this way you can always get a quick access to it.
You can simply add a tag to the tasks with high priority. This way you can click on the tag and a quick screen will pull all the tags with the priority. You can favourite that search to keep it at hand.
A third option would depend on how you build your project on ASANA:
If a project is small you can build the project in the order of task priorities. This way the layout is not driven by section but by priorities. Section could then be replaced by other custom fields.
I hope this helps.