Having strongboxes be bank only was something that was originally planned for EQ2 at launch. Unfortunately they couldn't get the code for making strongboxes bank only working, and just left it as is.
Perhaps the best solution is either to make Strong Boxes weigh significantly less than they do, or make bags = boxes minus two slots. It will still be win/win for tailors compared to now.
One concern I have is that other bags are suddenly going to reduce in value. I can see the following bags no longer worth the time or money to acquire, at least at level 90 (and perhaps even at level 80):
* Bag of Sewn Evil Eye* Bag of the Tinkerers* Box of Nil Space* Wantia Artisan's Satchel* Large Collector's Pouch* Huge Collector's Pouch* Dirby's Work Satchel* Any and every low level quested backpack or bag.
Keep in mind, carpenters have many, many more items that sell than tailors besides just boxes and bags. The market for tailor goods at high levels is limited: Once players outlevel mastercrafted gear and acquire gear upgrades, tailored armor ceases to be useful. On the other hand there's always a market for even level 1 carpenter furniture.