Even Minix 3 is fairly small. "Operating Systems: Design and Implementation" was synced with Minix 3 in its latest edition (2006). It's all the crud in later releases where things started getting junked up, after Tanenbaum got a windfall of cash, gave his students the keys to the kingdom, so they ended up importing large parts of NetBSD, sloppily. Say hello to 3-hour build times and a codebase that no one contributes to anymore.
Yeah after I read OSTEP and felt like I understood xv6 enough I tried to move on to minix 3 and reading tanenbaums book. I couldn't do it. There was just so much going on.