Lil. In this case, the number of obelisks required to unlock the map should be reduced to 6, so that it makes at least some sense. And with your "change," you won't even achieve that by the sixth week, because the game will be over by then.
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Spending several days on excavations is a loss of tempo. You still need to transport it and place it, and you put it there so nicely, but on the seventh day, your opponent overwhelms you because while you were digging for the Grail, the opponent had already taken over the map.

In the current version, do you need to visit absolutely all the obelisks on the map to unlock the full map, or is it enough to visit only some of them?

With my proposed option, you can reduce not the number of obelisks on the map, but the number of obelisks that need to be visited to obtain the map with the cross, to, say, 8-10 (and then fine-tune it during testing). The Grail should not be a means of achieving victory, but only one of the strategic options that can be used under certain circumstances, something like, "managed to win thanks to archdevils." There are very few such reports and games, but the strategic option exists, and the same applies to the Grail.
Spending several days on excavations is a loss of tempo – that's really "lame." Or do all 8 heroes, led by the boss, go on excavations? It's like an archaeological expedition. The "opponent comes on the 7th day" is also from the same category.