I dunno.
Even slow movers in bad shape are a problem in numbers.
So, carefully eliminating individuals before they can turn into a horde should be the default.
Once you get enough living together, you fortify and get snipers trained up. Set up on the walls first and pick off anything undead that comes close. Slowly set up an expanding circle of raised emplacements with sniper observers to pick off individuals at a longer distance from the settlement, and give warning for any hordes as well as being able to thin out a horde as it gets closer, and continue depleting the horde if they surround the settlement.
But, for lone travelers, assuming that you have a ranged weapon that’s quiet enough, always take them out. You never, ever leave an enemy behind you if you can take them out without causing a worse problem.
I think that’s the key to long term zombie survival. You have to take every reasonable opportunity to reduce the spread of the agent that’s causing it. Literal walking dead zombies, they’re all a disease vector. Every one you put down makes future survival easier. So it’s a calculated risk. Measure the risk of your infection in the attempt, measure the risk of attracting any unseen zombies, and if those risks are low to zero, it’s going to be a long term benefit to take one out.
Obviously, in a WD scenario, firearms increase the risk significantly compared to quieter weapons. But there are other options available, including the old and trusty Pointy Stick™. Even the roughest spear you can make gives you the reach to make a quick finish to slow zombies 1v1 with very low risk of contact, so you only have to worry about being capable of moving faster if the weapon fails.
Bows can replace firearms at that kind of range, as long as you practice, and it takes the risk down to zero for a single shot, since the noise a miss will make is in a different direction than you.
You’re right though, don’t fight. Assassinate.
Bodies don’t actually burn well at all. Even dried out bodies more smolder (people used to burn mummies, among other really silly things they did to them) than burn.
So, you can definitely make a pyre to make sure any flesh is gone, but the zombies won’t make good fuel.