If you account for the taper, the Neo has about 50% more volume than the 12”

I sometimes travel with backpack only (cheap European airlines) and that is a big difference.

I'm on Sequoia (v15.7.4). I have the original 2015 model (1.1Ghz Core M-5Y31, 8GB of RAM). It's a little slow, but fine for what I use it for (web browser, syncing music/photos to/from my phone, simple coding tasks). My main gripe is the battery only has 60% of its original capacity. Apple won't replace the battery, and doing it yourself is pretty tricky. At some point it'll break or no longer get security updates, and then I'll probably get a MacBook Air.

If you're using OpenCore Patcher, it's important to install the root patches to enable graphics acceleration. Otherwise it'll be ridiculously slow.

By dimensions, assuming the 2015 ("eleven year old") version, the 13" M4 MBA is 0.17" wider, 0.9" deeper, and 0.32 lbs heavier. Where it's harder to compare is thickness. The M4 is 0.44" thick where the Intel one was tapered (0.11"-0.68").

Kind of hard to see that as "HUGE" in comparison. Bigger? Yes, but not really huge.