To reply to A, you really seem to understand very little about batteries, you could easily put a 99Wh battery (max allowed) in it while staying under 1kg and no, there is no way you can have a 300 gr laptop of this size without a battery. Battery is around 10-15% of the weight, but you have no clue.
What's more, the concept of being plugged in is changed with full USB power delivery, as my galaxy s7 quick charger can keep my notebook 9 charged for most use scenarios. No comparison with a normal laptop charger. Just a phone charger. Same thing with a small quick charge power bank. So when you need more than its 5-6 hours you can double, triple etc the battery with one or more compact power banks and the rest of the time have the lightest laptop you can get...

Battery technology may seem like a standstill but has actually come a long way in terms of price and mass density. A high quality 8-cell 100 Wh Lithium-Polymer battery used on laptops today is only around 180-200 g. Cost is not an obstacle either from a per unit perspective. This trend for thinner and lighter devices is nonsensical, at least until we can practically implement a much more efficient cell technology into mobile devices.

On a side note, Samsung and LG offers 2 / 3 different lines of identically named  laptops sorted by their battery capacity and in turn, weight. For instance in South Korea, LG's top of the line Gram series has 2 separate "All-Day" and "Ultra-Light" models for all 13, 14 and 15" laptops depending on their batteries. This is also the case for Samsung's own Notebook 9 series and some of their rather unknown mid-range and low-end laptops limited to Korean mainland.

From most reviews I have seen, weight is directly proportional with the battery capacity. I can make a 300g laptop by using a 10Wh battery - but would you be interested in using it? Wait, if you are willing to use it only plugged (as I am using my 2005-era laptop right now, because its battery no longer retains charge for more than 20 minutes), then I can make it even lighter!

" noticeably lighter"? My Samsung Notebook 9 (i7 16GB RAM) is 788gr (30gr lighter than what you say). Surface pro 3 is 811gr (heavier than what MS says) in the same scale...  I don't think you would feel the around 30 gr difference with the Samsung.... Anyway what a pity it's only sold in Japan