The frequency adjustment system just randomly selects cards but with cards with higher scores coming up more often - it doesn't do any special magic to ensure that you see all of the cards you haven't seen in a while, or prioritize cards by anything other than their scores. (this is why I keep murmuring about removing it - I don't really feel like it offers any benefit over spaced repetition at this point because it's too random) So it's not a good idea to hang a spaced-repetition-optimizing system on that.
My problem with the card limit wasn't that you'll occasionally have a few days where you miss / have to study more (or review cards a bit late) to catch up, my problem with it is that people might keep falling farther and farther behind; decide they only want to study 100 cards a day and eventually be reviewing cards weeks after they're due. Yes, the manual might specifically tell you that you shouldn't do that / should only do that for a few days, but people wouldn't read it or would ignore its advice and weeks later they'd be wondering why they were having such a touch time remembering vocabulary. We still have to prioritize cards based on how far past due they are - otherwise, even if you were only a little behind you could still end up having a card's review get delayed a week because it would keep not showing up.
My 120 card example was operating on the assumption that you had so many old cards to review that the combination of those plus cards answered incorrectly from previous sessions would keep you at 120 per day (even assuming no new cards) - if the maximum score is at 10000 and you're reviewing even the highest-score cards every 100 days, having 12000 old cards (not at all out of line for some people) would leave you with 120 per day even if you kept answering everything correctly and didn't add any new ones. Now you can argue that we ought to have a higher maximum score by default, and we probably should, but then again a lot of people aren't even taking the time to review 50 cards a day, let alone 100.
I think the best solution to this problem might be to simply make "limit unlearned" also check for the number of cards currently due for review and refuse to introduce new cards if it was above a certain limit; combine that with a more user-friendly system for redistributing / extending the timelines of some cards (already supported through the Batch screen, but most people don't know about that), a slightly more flexible interval check that looks ahead to the next few days and brings some cards forward / pushes some cards back to even things out, and a higher maximum score (which we'd automatically re-set for everyone but then allow people to back and change again) and we could make vocabulary pile-ups much less of a problem than they are now. The redistribution system could be really beautifully done - a bar below the session start button telling you how many cards you had due, a button below that allowing you to redistribute some cards, a count of the number of times you'd done that recently / alert if it was too many, etc - and would be completely transparent, but having it be a button instead of a set-it-and-forget-it number-of-cards count would make it clear that this would be destructive to your word retention if done too often.