1. Lack of USB-C ports means I wouldn't be able to safely use any USB-C only peripherals (since the USB spec explicitly bans adapters in that direction)
2. Lack of security updates for firmware, microcode, etc.
3. Hard to find replacement batteries from reputable sources
4. The CPU and memory requirements of software are steadily increasing
1. which devices are those? USB-C is a type of plug. it does not define the USB standard that runs on it. so if i understand that correctly, there can't be a USB-C only device. USB4 is defined to run only on USB-C, but it is also defined to be backwards compatible to at least USB3.x. the spec forbids certain legacy adapters, but only because it would allow for to many invalid and potentially unsafe cable connections. the same connection can be made to work with a direct cable that allows the connection of a USB-C device to a legacy port. and even a 10 year old laptop should at least support USB3.0.
2+3. depends on the specific devices.
4. 10-15 years ago maybe that was still true. but the power and speed of devices no longer increases at the same rate. it has slowed down to the point that a 6 year old laptop performs just as well for my daily tasks as a 2 year old one and i run the same OS on both. the difference is only noticeable for modern games and some CPU/GPU intensive tasks. i also remember the same experience with even older laptops (i don't have one here right now, so i can't compare directly). what made the older laptops slower/less powerful was less RAM.
For point 1, consider a flash drive with only a USB-C connector on it. The kind of adapter that you'd need to plug that into a laptop with only USB-A ports is exactly the kind that the spec forbids.
My understanding is that they're "fine" if you only use them "correctly", and that the reason they're forbidden is that it's so easy to plug things into them in ways that will create a short circuit (e.g., plugging the C end of an A-to-C cable into one).
you don't need any adapter. all my USB-C drives come with a cable that has C on one end and A on the other. again, those cables are allowed. only adapters that would allow you to use a C-C cable may not be. so connecting a USB-C drive to an old laptop that only has USB-A plugs is fine, and is supported.
oh, ok, those seem to be rare though, and personally i find them impractical because the C connector makes them less stable. with an A connector the flash drive can be so small that it almost fits inside the connector entirely. in other words, buying a device that can't handle these flash drives would be a tradeoff that doesn't have much of a downside unless i already have such a drive that i really want to use.
but if i have a tendency to buy older devices, then i likely also have a tendency to avoid getting such modern drives. they will be coming though, thanks to USB4, and there will be a day where i can't avoid needing a laptop with at least two USB-C ports (because one of them will be used for charging), or get a USB4 rated USB-C only hub. and hopefully by then even older laptops will already have at least one USB-C port too (even if it doesn't support USB4 yet).
3. I am always doing a little research before I replace a battery but so far every replacement for a old ThinkPad had way better results as expected, very likely better than a good 'original' is at this point.
4. Not sure if I can agree. Most software I use just got more efficient over the years. Only exception being the IDE or code editor. #justlinuxthings
Lol! Finding a bunch of good 18650s is WAY easier than a freaking proprietary black bar. Replacing them requires some skill, though, but most repair shops can or know who can do it properly.
1. Lack of USB-C ports means I wouldn't be able to safely use any USB-C only peripherals (since the USB spec explicitly bans adapters in that direction)
2. Lack of security updates for firmware, microcode, etc.
3. Hard to find replacement batteries from reputable sources
4. The CPU and memory requirements of software are steadily increasing