I've spent all my stash pages ages ago and have multiple mules as well. It's suffering.
And this shit is triple retarded in Grim Dawn. Lets compare Grim Dawn to Path of Exile where you also have limited stash space. In Path of Exile, there is an essential multiplayer component. You can play the whole game solo, but the moment you start the game, you are online anyway and are able to trade with other players relatively easy, there is even a dedicated trade chat for it. So in such circumstances, a limited stash space is justified a bit by the fact that if you had unlimited space, it would, albeit in a small way discourage selling your trash to get more space. There is no such concerns in Grim Dawn, there you need to create multiplayer session to even play with other players, and there is no trade chat, and trading in general is not very popular and widely used.
Another aspect is the price. Path of Exile is completly free to download and play, and they use the limited stash tab as a way to get some money from the users who would like more convinience (Not having to have many mules etc.) and are willing to pay a few dollars for additional stash tabs. Thats their justification for limiting the available stash tabs. In Grim Dawn, you pay the full price for the game so you should be given all the convinience you would like.
Also, Path of Exile gives you 4 stash tabs, but they are bigger than the ones in Grim Dawn. What is more, Grim Dawn clutters your stash space with all of the rare/nonrare components which are an essential system of upgrading and crafting gear. To make this clutter even bigger, there is a random stat rolled on completion of every component, so you will have 20 different serrated spikes. And finally, nothing (Except some few crafting materials) fucking stacks in Grim Dawn, every finished component takes its own square in stash space because they have this random stat roll on them.
What Crate could do? Introduce some kind of component bags that you could put in your stash, they could take 4 squares of space and would hold an infinite amount of components. That way, we could simply dump all of our components into them, or have separate bags for rare/nonrare components, or melee/ranged components, or any other way our autistic brain wants. That would clear a fair amount of stash space and would fundamentaly change nothing about the game.
Adherance to an old system just because Titan Quest had it too, is a retarded idea, especially in a game where you pay the full price for the game, and trading isnt a major part.