My rule of thumb is are they selling your work briskly? If they are doing a great job selling your work, you may be able to find another gallery far away to start selling work as well at better commission rates. Your work should be selling and in the marketplace to increase prices long term. If this 50/50 gallery is selling work and you don’t have to pay to show, that’s not bad as long as they are moving the work. As you get better known, you can negociate a better split.
The best example is Damien Hirst. He was selling well in UK galleries, but still had the bulk of his best work. Then after he was well-established, he went around the galleries to the auction houses and lowered his cost from the 60/40 down to the 3% of auction houses. Now for the majority of artists, they just aren’t going to reach Hirst demand to try that. A gallery does do marketing and selling for you while you work.
Another thing is that for the gallery split you can build their split into your price, so you don’t feel ripped off. Just remember galleries are offering a valuable service of selling while you paint.
I think focusing on getting your work into multiple cities and doing your own marketing will help bring up your prices, so you can afford the 50/50 split or bargain for a lower split elsewhere. No marketing leads to low sales and low prices long-term.