I understand the interpretation, but I started off by asking this question and got the specific answer of most spells known. I gave four different ideas of what they could mean by the question, with one of them being the most spells known and tying that to a high level wizard getting every wizard spell, and they said that was what they meant.
Dragonmarks specifically give you more spells known - the mark of handling gives a bunch of druid spells, which is why it seemed the best choice if you are doing this. It does give two of those spells as a per short rest thing, but that doesn't do any more than starting as a fairy or genasi would. If we say most spells that can be cast at a moment's notice, then those would be better than dragonmarked, because they give two spells and a cantrip, instead of just two spells.
I think the most persuasive evidence, though, is that one of the options I gave was the total number of spell slots one could use in a day. That one broke clearly for a Wiz 18, because at that level they get spell mastery, and could conceivably fire off a trio of magic missiles every 6 seconds, or become nightcrawler by misty stepping every 6 seconds (FTR, this is a nightmare that is coming to me when the bladesinger in our group hits level 18 - I have no doubt that he will take misty step for mastery, and he will use it for pretty close to every bonus action he takes.)
I could be wrong, of course - already have been in this thread when I misread a table. Trickster and I may just not have communicated well. But if so, the conclusions thus far may be wrong and need to be looked at closer.