It might help if you used a computer with CPU horsepower that actually exists.
And in case this sounded facetious, any reasonable CPU from the past 15 years can handle software decoding of high resolution video just fine.
This all said however, if you do actually need full use of all hardware resources then being constrained to software is certainly a factor worth considering.
Brute force helps a lot, but do you want a ≥5GHz multi-core CPU burning 150W just to watch a single video stream with maximum paranoia settings?
I mean, yes?
We're not talking about bloat here, you're deliberately imposing significant overhead load for a specific purpose.
You can't really subsequently complain about performance unless you bring sufficiently powerful hardware to compensate for that overhead.
4k VP9 from youtube takes my 5950x around 20-25% CPU usage to handle with hardware acceleration disabled.
The fastest consumer CPU available 15 years ago could not handle that. Hell, even CPUs from 10 years ago couldn't do that. Add power & thermal limitations of a laptop CPU? Not a chance.
And that's just VP9! HEVC or AV1 would really put the hurt on.
To be pedantic, OP specified "HD" which is 720p. I gave him benefit of the doubt by saying "high resolution" in my reply, but I think 4K is unreasonable given the provided context. I'd wager 1080p ("Full HD") at most. There's also the question of frame rate, though we can probably safely assume either 29.976 or 59.952 fps since it's Youtube.
As an aside, software decoding performance can vary pretty significantly depending on the codec used for both encoding and decoding. Bit of a history lesson, CoreAVC was infamous for being very easy on the CPU compared to other h.264 decoders like ffmpeg.
It often helped to actually give the VM more cores (not just the default 2), but sometimes it was due to some weirdo codec/quality setting, and recoding the video just solved it. Sometimes switching to vlc (from mplayer) helped. Other times it was simply due to the sys-usb vm being overloaded.