You post is long but is not very clear, the commenter above is correct. What exactly is your grievance? That Linux does not support your ancient laptop? Or it does not support the laptops (let’s face it, tablets) that YOU want?
Unfortunately resources are scarce in the Linux community, so labor needs to be allocated where most people are (AKA using hardware from the last ~5-10 years, not 30). And Windows surface tablets are extremely locked down.
I’m sorry that you can’t find people who want to continue supporting hardware so old people get nostalgia when they hear its name (eg. Pentium i586). It seems to me you’re not willing to do it either.
Ultimately you’re reducing to hardware a phenomenon that also involves software. Realistically who can run modern computing operations (such as web browsering) on a laptop with 3-4 GB RAM? The answer is nobody. Not comfortably, at least. Browsers take easily 3GB of RAM with just a few tabs open.
As for all laptops being bulky… this is the consumer preference. I don’t like it either but we can barely fault manufacturers for producing what consumers want to buy. I see this trend on phones as well, for me smaller phones are the best thing but the market moved towards bigger screens, heavier phones. And you want underpowered devices? If you could have a slim and lightweight laptop/tablet, wouldn’t you want it to be as powerful as possible? This doesn’t make any sense from a consumer perspective.
Lastly, if you want whatever machine you buy to last longer, then ironically you should learn a thing or two about hardware so that you can replace parts yourself. You don’t have to become a genius, just follow some steps on YouTube on how to change RAM, add SSDs… and yes, Thinkpads especially older ones are great for this since many parts are non-soldered. Apparently this year they are also launching a new one that is way easier to open up and replace parts with their removable keyboard.