Sorry, I don't have any strong "analog vs digital" leanings (more of a writer and a player than a techie) but I would suggest the "input-to-track architecture" you describe is not unique to the digital domain and goes back a little further than the last 15 years. For example, I started out on a Tascam 234, and subsequently owned and used a Fostex X-15, a Yamaha MT2X, two more 234s, a Porta-02, and most recently a 424mkiii. None of them had on board front-end mix capacity (that I was aware of), and so I've never expected it from a 4-track tape deck. To me it's unusual in that I've seen more decks without it than with it.
The 234 doesn't have a built-in mixer, so that doesn't apply. I haven't used the Porta-02 (I don't think), so I can't speak for that, but the 424mkiii most certainly has that capability. It, along with the 414, has the ability to record in
direct mode (i.e., CH 1 input to TRK 1) or
buss mode (i.e., CH 1 input to which track you want it depending on how you pan the input). In fact, you can see it right here on the front page of the 424mkiii manual in the Record Function section. Each track has a three-position switch for DIRECT, SAFE (no record), or BUSS (L for odd and R for even).
Hm, maybe I could have phrased that better.. But mixing out front, you're stuck with your decisions. I get how premixing six mics to two tracks can be critical when you're dealing with track restrictions, but with a simple stereo pair guess I don't see the point of limiting yourself by pre-panning anything.
You're misunderstanding this. It has nothing to do with mixing, really. You're not stuck with anything, any more than you're stuck with a single guitar on TRK 1 if you record it directly to it with the CH 1 input. All it's doing is giving you the option, for example, to use all four inputs (or even all six inputs on some machine) to
pre-mix (not mix) a bunch of instruments onto one track instead of having to use an external sub-mixer for that purpose.
Once you record those 4 instruments (let's say it's a rhythm guitar, bongos, triangle, and shaker) to TRK 1, you can freely pan that track anywhere you want when you mix the song down.
Again, I don't know of any machine that allows direct-to-track recording and doesn't also allow buss recording. The
only reason you'd need direct-to-track recording is if you're recording all four tracks at once. If you're recording only one or two tracks at once, then buss mode and direct mode will both accomplish the same exact thing.
The difference is, again, when you want to premix something. Let's say you're tracking a drum kit with 4 mics and you want them to be on a stereo pair of Tracks 1 and 2. If your machine
didn't have a buss mode, you'd have to use an external mic mixer to do this because you would have four mics that need to be mixed down to two channels. So you'd plug your four mics into it and adjust the panning/level of each, then send the two L-R cables out of it and into the CH 1 and 2 inputs of your 4 track.
With buss mode, though, you don't need the external mixer at all to accomplish the same thing. You just plug the 4 mics into the CH 1-4 inputs, adjust the level and panning, and set TRK 1 to record buss L and TRK 2 to record buss R. Same exact result, but no external mixer needed!