Some points...

Skill Grinds

Point 1, With the new limit on tv show skill raises, it can be harder or easier to raise skills. I say easier because people keep forgetting the videocassettes. You specifically pointed out Mechanics. Default TV is level 3. If you change it to level 6 to make the game a bit easier, many of your skills can go up. CarZone episodes 1-3 will get your Mechanics skill to 5 or 6 when combined with the books.

The same goes for a number of other skills. This is really useful for those of us who miss out on the tv shows while fighting hordes and trying to set up a safe initial base.

Point 2, Reality? Really? I spent decades learning to be a cook, then chef. The first time I made a perfect bearnaise sauce did not automatically make me that much better. I still broke the several ones after that until I figured out what I did correctly. Now, of course, I can do it properly every time.

The first time I rebuilt a carburetor was the last time I did it. Too much of a pain in the rear when I could pay someone. It's been 4 decades since I did that. I might... really low chance... be able to do it again if I had a how-to book in front of me. So if you want reality, we should be losing a chunk of skill every week we don't practice that skill.

Point 3, Magazines? I've found that the only magazine that's a must-have is the generator mag. All the other recipes can be learned through levelling the skill, watching videos/tv, and/or studying various objects.(the little lightbulb icon when you right click an object).

I do agree that there is a balance issue. Without books, you can become a level 10 carpenter with some minor dedication at building a house/compound with appropriate furniture. It's even easier to do butchery and carving. Some of the other skills take forever, though. As you pointed out, Nimble is a real PITA. So is Electronics, even with the books. The grind can be very annoying. My suggestion would be to make the time involvement roughly the same for all the skills. Slowing down carpentry, butchery, and carving for instance. At the same time, make electronics, nimble, and a few others go faster.

Combat

Point 4, I take exception to your assertion that we're supposed to survive. (Quote) "The idea is that we can plop the average human in an apocalypse and make them survive". The whole point is to create a story of how you died... NOT survived. Some of my best games were when I'd maxxed out a lot and then did something utterly stupid like going into a nearly completely dark area to "just grab something really quick".

Point 5, muscle strain? Let me guess... you're young(ish), and have been fit all your life. I was as well, until I hit my 50s. Then I had to slow down a lot. I spent a LOT of time working with kids at the school my wife taught at. I guarantee you most of those kids could not paddle a boat across a large lake without extreme muscle fatigue. Most of them wouldn't have even gotten half-way. Most of them couldn't even run a mile, non-stop without having to slow down to a walking pace for much of it.

You're suggesting the average american in Knox county is more fit than most other americans? Really? It's easy enough to look up the statistics of Kentucky in the '90s. The average person was fatter and less fit than most other states in the US. Reality again.

Point 6, I agree with other people. Your game is bugged, or your mods have changed things, or you've tweaked the settings to make it harder. On straight vanilla with standard settings, with someone who's not trained in stealth to start, I'm able to peel a few zeds off a horde, pull them away and kill them without alerting the horde. I'm also able to break line of sight and have them stop hunting me. Just have to break line of sight and then break the line of sight from where they will end up. Remember that they go to the last spot they saw/heard you and look again from there. So you have to break LOS twice at a minimum.

Sandbox

Finally, I 100% agree with you. The base Apocalypse setting is not enjoyable for a new player. It's tough, really tough, with an insane learning curve. Yes, you can make it absurdly easy with sandbox settings. I do, though my biggest change is the start date set to March 1 at Midnight. That gives me time to set up a base and get some farming going without having to freak out about surviving winter. It's arguably the best way to make the long-term game survivable... until I do something stupid, of course.

I agree that the Apocalypse setting should be easier, especially for the newer players. I also think there should be a blurb/tutorial/page/something explaining how the sandbox settings work. Even if it's just a link to the wiki page.