As for the animal empathy/beast mastery; I'm not going to say that every Ranger must have one (I know too many would disagree with that statement), but I will say that there needs to be at least the option for it, and in a way superior to simply a animal pet that anyone else picks up. Just as importantly, you need to have the option of having a magic-using beastmaster together.
So, if you treat animal companions as party members, you still have the option of having an animal companion, and you absolutely have the option of having a magic-using character with a beast ally. In fact, your options for what that might look like are significantly expanded. Additionally, if you focus your resources on buffing spells that you grant to your pet, your allied NPC will be significantly better than, say, the evoker's.
What this proposal doesn't do is make your animal companion better than anyone else's. This hasn't been something the ranger has had in any edition (including 5e - a fighter with a wolf NPC trumps a beastmaster with a wolf companion; a beastmaster with a wolf companion AND a wolf NPC...still probably isn't better with their companion than the fighter with a wolf NPC), so I don't know that that's a criteria I'd personally require a ranger's companion to meet. I get that your requirement is different, but it doesn't seem like there's any extant version of the ranger that gives you that.
And that's the problem. You've taken away a defining feature so that its no longer part of their identity. Furthermore, its everyone "has the potential if the GM allows it, which she may not." Its no longer a benefit of being a Ranger, and more something that's at the grace of your GM, which is a bad assumption to make.
I don't know that I can agree with the assertion that a ranger's animal companion specifically is a bigger part of their identity than a druid's animal companion or a paladin's mount or a summoner's demon buddy or a wizard's familiar is to their identity. Given the historical D&D ranger, that simply doesn't seem to be the case in general.
- At the ranger's conception in the Strategic Review, they didn't have an animal companion. The closest they get is a chance to have unicorns, pegasi, and wearbears as followers. (ie, only at high level, if the DM allows it, and they're generally not there for adventuring with)
- In 1e, the ranger didn't have an animal companion. The closest they get is a chance to have bears, lynxes, owls, and a blink dog (among more exotic creatures) as followers. (ie, only at high level, if the DM allows it, and they're generally not there for adventuring with)
- In 2e, the ranger didn't have an animal companion. The closest they get is a chance to have bears, dogs, falcons, great cats, and ravens (among more exotic creatures) as followers. There was a ranger kit, the beastmaster, which is the first indication in D&D of any type of ranger that has a close bond with an animal companion (or henchmen, in their case). Notably, his beastmaster was able to split XP with their animal henchmen, advancing them as fighters - the most direct translation of this would be to treat them as NPC party members in 5e. Also of interest might be the Falconer kit (gained a falcon as a follower) and the Mountain Man kit (might gain a bear as a follower). We're still well within the realm of treating these as NPC hirelings of some sort.
- In 3e, the ranger had an animal companion. It was a weak version of the druid's animal companion, and thus was very much not suitable for combat in most situations. Various prestige classes, feats, or other options, many of them open to druids as well, enhanced this "noncombat companion."
- In 4e, the original ranger had neither animal companions, nor spells. A beast mastery build was added, where the ranger gave up actions to allow their companion to attack. Later, a spell-using ranger was added, but it does not have any animal companion.
I have. The variant makes up for its loss of magic by giving the Ranger maneuvers taken from the Fighter. There's still some parts of the Ranger that the Fighter doesn't touch at this point. However, stripping away the animal empathy aspects as well, is a lot - that leaves wilderness survival and skirmishing. Fighters can get wilderness skills from a background now and match the Ranger there, and the Fighter can turn to skirmishing with the right selection of feats and weaponry.
So is a spell-less ranger who chooses the Hunter subclass the same as a fighter in your eyes? If so, I don't think I can agree with that assumption, either.
When you give the Fighter the ability to have an animal pet, wilderness survival skills and techniques, skirmish ability, and remove the magic from a Ranger... suddenly, the difference between the two is so minimal, there's no realistic reason to have a separate class anymore.
An eldritch knight can take a background and get an NPC party member and can take the Archery or TWF fighting styles and we have a spell-using Fighter with an animal pet, wilderness survival techniques, and skirmishing ability. You could even include multiclass rules and instead of an eldritch knight, I can be a fighter/druid. I'd be better with my companion than the beastmaster ranger would be, too, since it would operate independently. I can do that
today. So is it the case that in D&D 5e today, the difference between the fighter and the ranger is minimal, and there's no reason to have two separate classes anymore?
Personally, I don't think so. It is not the animal friend and the spellcasting that gives rangers their identity. You can take either one, or both, away from the ranger and still have a "ranger." There's been rangers throughout D&D history that have not had one or the other or both, and they were still rangers.
Where is the panther coming from, is it "my" benefit, or something that suffers the whim of the DM? Because, if the latter is ever true, then no, that is a terrible beastmaster replacement. The sense of connection is not there.
A beastmaster's beast companion currently suffers at the whim of a DM (because they are not very hard to kill, if nothing else). Is the current beastmaster a terrible beastmaster because you can't connect to your animal companion?
You've said that spells and an animal buddy are key to your concept of a ranger. Imagine being a Sylvan ranger (so spells like an EK, but druid-y) with a load out of buff spells enhancing the attacks of your panther. How does that image differ from what you'd imagine a ranger to be?