True, but's how it's been since the game started.
When I first started playing the game, I remember reading "beginner guides" that recommended dumping excess gold into walls, and "banking" elixir by queuing up expensive troops in the barracks. That's just how the game was and always has been. You could basically dump most of your gold, depending on what level walls you had available to upgrade. And you could hide a substantial amount of elixir. For a high level town hall, it's not enough elixir for a major upgrade, but at least enough to fund a minor upgrade or pay for a clan war army. And for a TH4 or TH5, it really could be enough for a major upgrade.
So I'm not looking to change how gold is spent on walls. I'm just looking for a way to make elixir walls available without ruining the whole economy for TH9's and TH10's. My preferred method is to set a reserve (Goobers has a thread on that topic). My next preference is to make elixir walls more expensive than gold (see for example
this post). Someone had a suggestion to make level 9 walls available at TH8, and I think that idea has merit as well. I don't know how much that will disrupt the balance between TH7's and TH8's, or the balance between TH8's and TH9's, but I assume the disruption, if any, will be limited in scope, simply because so few players bother to max walls before upgrading.
And in the current thread, I don't think time-only walls are a good idea. But maybe adding a moderate time penalty to elixir walls (a hybrid approach) might be a good idea. It's at least worth tossing the idea around. So I put it out there. If the idea sucks, it sucks, but I wanted to at least toss it out for discussion.