That page only lists browser engines it thinks are “notable”, which is not the same as viable. Microsoft stopped developing its own engines when it moved Edge to Blink.

Currently there are four viable browser engines (still being developed and capable of displaying enough sites with enough accuracy to make a plausible daily driver) in two families: WebKit and its fork Blink, and Gecko and its fork Goanna. Goanna is not corporate. In addition, there are some experimental engines, like Ladybird’s.

I won’t deny that the situation is dire, but it isn’t quite as bad as you’ve painted it. Yet.

I think part of what you’re missing may be a set of very old assumptions about where the danger is coming from.

Linux was modeled after UNIX, and much of its core software was ported from other UNIX versions, or at least written in imitation of their utilities. UNIX was designed to be installed on large pre-Internet multi-user mainframe+dumb terminal systems in industry or post-secondary education. So there’s an underlying assumption that a system is likely to have multiple human users, most of whom are not involved in maintaining the system, some of whom may be hostile to each other or to the owner of the system (think student pranks or disgruntled employees), and they all log in at once. Under those circumstances, users need to be protected from each other, and the system needs to be protected from malicious users. That’s where the system of user and root passwords is coming from: it’s trying to deal with an internal threat model, although separating some software into its own accounts also allows the system to be deployed against external threats. Over the years, other things have been layered on top of the base model, but if you scratch the paint off, you’ll find it there underneath.

Windows, on the other hand, was built for PCs, and more or less assumes that only one user can be logged in to a machine at a time. Windows security is concerned almost entirely with external threats: viruses and other malware, remote access, etc. User-versus-user situations are a very minor concern. It’s also a much more recent creation—Windows had essentially no security until the Internet had become well-established and Microsoft’s poor early choices about macros and scripts came back to bite them on the buttocks.

So it isn’t so much that one is more secure than the other as that they started with different threat models and come from different periods of computing history.

Gentoo normally keeps arches for as long as the kernel still supports them, although package testing for some of the rarer ones may be limited. 32-bit Intel is still treated as a major arch and receives the full set of tests and package stabilizations.

Your worst problem is going to be web browsers. Chrome and derivatives don’t run on 32-bit, and Firefox is supposed to be dropping support. If Seamonkey follows Firefox, that leaves you with Pale Moon as the only reasonably maintained option.