KDE uses less RAM, you can fact check quite easily.
Depending on the distro it ships with more or less stuff, but a few games, an office suite, media players for audio/video and in some cases a partition manager, are all necessary tools in any setup, at least in my book.
I don't see the bloat.
Buy new router, connect via Ethernet, disable ISP's router Wifi to avoid radio interference, share wifi access to family member.
Set QoS rules on your new router to get a higher priority/bandwidth for YOUR devices.