Why did they have to remove S3 sleep anyway? At least it worked. What was wrong with S3 sleep? Hardware support? At least it didn't set your backpack on fire. LTT made a video about your very problem.
I would honestly just use shutdown.
#BringBackS3Sleep
Mine supports s2idle [deep], and it's 6 years old.
On Windows, make sure to unplug the charger before closing the lid, otherwise it'll try to run Windows updates because it thinks it on AC power.
And? Windows 7 shits itself on UEFI systems. It's in a sort of limbo when it comes to UEFI support. It has a UEFI compatible version of Windows Boot Manager, but it'll usually hang the computer as soon as it's done booting.
For your last thing, the only thing that can do that is a firmware update.
I literally reinstalled Windows yesterday and systemd-boot went nowhere. Something's wrong with your UEFI implementation. Another laptop I have (HP 2000 Notebook PC, will ALWAYS boot the Microsoft folder if it exists, and there's no ESP. I had to rename the folder.
And by "corrupt the UEFI", do you really know what you're talking about? It's the ESP that contains the bootloaders.
It's objectively better. Rather than having to manipulate raw bytes to change my bootloader, I can just add it to my ESP, which is a partition that the UEFI reads to find what to start on your hard disk. Also, no more 640x480 resolution at boot.
All computers since the late-Windows 7 era use UEFI.
Unplug the charger BEFORE you close the lid.