You answered your own question in the last paragraph. Yes to hit DM in a year would be 300 + 600 + 1200
There is a way to lose lesser miles
Call MPC to see if they can grant you Silver at 260 after taking one trip with the second trip booking confined.
After being reset for Silver, you can take two more trips which will give you 520, call MPC to early upgrade you after you have a confirmed booking for the third trip, or fly OW regionally in your home location and credit to MPC.
After uograde to GO, take 4 more trips to hit 1040 and with both outbound legs flown for your trip 5, they might be able to upgrade you if you get to 1170
caveat, YMMV