They are not a bad starting point, but as all the draft homebrew rules, they feels a little clunky and unclear. For example, I honestly don't understand the "healing save" mechanics. Also, as a personal preference, I would remove the "rally" rest mechanics and simply make the rest mechanics a little less punishing, so that they can also work for "dungeon delving" without too much trouble. In Symbaroum, encounters are often much less frequent than in D&D and much more interesting even when dungeon delving (thank god for that, I really hate how many D&D encounters feel like fillers just for draining a party's resources otherwise they will annihilate the "boss") so I think is fine to balance resting with this assumption in mind
The Healing Save occurs when a character is healed by any amount, and allows you to roll a d20 + the amount healed, against a DC 20, if you succeed, you may remove either a point of exhaustion or a death save failure.
As mentioned the resting mechanics are either balance for an extended dungeon crawl with many encounters before a long rest, or they are balanced for sandbox exploration where there will be few encounters before a long rest (like Symbaroum). I believe it would be challenging to design a system to be optimized for both conditions, as they produce drastically different results.
Also, the 'punishing' core rest mechanics described here are basically the same as the current drafted rules for Symbaroum 5e; this was the basis for this document.
If the system gives more for free on rests then it removes the grittiness, and just approaches closer to 5e RAW, which is rest and everything is back to normal. We want to stay as far away from that as possible. The rally mechanic adds a tactical decision with a lasting consequence. The current 5e system is optimized for many encounters per long rest. These new rules are optimized for sandbox exploration, and much closer to Symbaroum RAW where you get very little back for free on rests, therefore they needed a release mechanism for extended forays that may still be present in a typical (non-Symbaroum) 5e campaign.
Of course you are free to home rule anything you like, this is just the reasoning behind these rules as written. Thanks for the feedback.