With new layout modes coming to CSS, including flex and grid, I don't think the statement "float-based & table-based layouts that have remained unimproved to this day" is fair.
Flexbox is a step forward, Grid Layout is awesome but is starting to look like CSS Vars, another spec lost in years of limbo
The myriad of incompatible CSS layout modes, present & coming, are evidence of the lack of a holistic & future-proof foundation. The Constraint CSS primitives can be used to implement Flexbox & Grid Layout in total, not true the other way around. And, such implementations would be fully compatible with each other. BTW, a Grid Layout implementation in GSS is well on its way.
The 2 fundamental layout features lacking in future CSS specs is 1) relative positioning & sizing & 2) true source order independence. Less this is addressed, layout will be tightly coupled with the DOM & good luck centering things
I'm all for improving what we have, and the new GSS system does look interesting and could possibly influence CSS. But I think you're reacting too strongly to CSS. AFAIK the normal, flex, and grid layout modes are compatible (in the sense that you can mix them in one page and have things like flex inside grid elements and vice versa). Being a lurker on some standardisation email lists some of the best engineers in the world are on there taking everything very seriously, including future-proofing since everyone is well aware anything they add now will basically have to be supported forever.
I'm not sure I understand your two complaints (isn't there already position: relative and percentage sizes?), but I think good engineering is always about making tradeoffs, and while I don't understand GSS enough to criticise it I feel it's unlikely to be a silver bullet that magically fixes everything in itself, and will likely have its own quirks and pitfalls as well.
