Firefox

I entirely agree with you about Google perpetually shifting the goalposts, which increases complexity and works to their advantage. I would say I think of the standards and technology as being, in many ways, integrally related.

I think the idea though, is that it has indeed grown so vast that you need, effectively, teams of teams to keep up. There are browsers done with small teams of developers, but the fruits of those, imo, are not super promising.

Opera: moved to Chromium.

Vivaldi: also on Chromium.

Midori: moved to Chromium.

Falkon: Developed by the KDE team. Perhaps the closest example to what you are thinking of. It's functional but lags well behind modern web standards.

Netsurf: Remarkable and inspiring small browser written from scratch, but well behind anything like a modern browsing experience.

Dillo: Amazing for what it is, breathing life into old laptops from the 90s, part of the incredible software ecosystem that makes Linux so remarkable, so capable of doing more with less. It's a web browser under a megabyte. Amazing for what it is, but can barely do more than browse text and display images with decent formatting.

Otter: An attempt to keep the Old Opera going, but well behind modern standards. Also probably pretty close to what you are suggesting.

Pale Moon: Interesting old fork of pre-quantum Firefox but again well behind modern web standards.

All of the examples have either moved to Chromium to keep up, or are well behind the curve of being modern browsers. If Firefox had the compromised functionality of Otter it might shed what modest market share it still has, not to mention get pilloried in comment sections here at Lemmy by aspiring conspiracy theorists.

I do love all of these projects and everything they stand for (well, the non-chromium ones at least) but the evidence out there suggests it's hard to do.