I hadn't really considered the angle of 'hey, I'll DM now so that I can launch a new character who's already min-maxed with magic items and feats, just the way I want it, and I won't even have to deal with the horribly inefficient low levels where I might decide the effort isn't worth it".
I think a lot of folks on this thread are overestimating how much "damage" a player can do with these new DM Rewards. It's true that someone could "cheat the system" by earning their 3000 xp for the social media tasks. That would put a character up to level 4, which isn't really all that high. They'd also be starting with 0 downtime, and so would have to play 2-4 DDEX or DDAL adventures before they would be eligible to "Catch Up" to Tier 2, and at that point they probably leveled up to level 5 through playing.
All of the other rewards require people to actually DM an adventure. As these rewards are meant to incentivize people to DM, I don't see why that's a problem. The particular reward that seems to be causing the most concern is the "Dedicated DM" reward, which allows a DM to gain a magic item. To recieve this reward, you must DM 7 DDAL/DDEX adventures. Assuming that the hypothetical person trying to game the system only runs the shortest adventures available, this is still a 14 hour investment in DMing, most likely spread across almost two months real time. While DMing these adventures, the player's characters are only earning about 1/4 of the xp of the PCs and is gaining a single "tier appropriate" magic item. Meanwhile, the other players (assuming a 7 player table) are all receiving full xp and, most likely, at least one magic item relevant for their class. These items are not necessarily "tier appropraite" - I ran DDEX3-7 a week or so ago, which is a Tier 2 adventure, and the magic item in the adventure was a Very Rare Oathbow. This item wouldn't be available for an equivalent DM Reward character unless it was Tier 3.
That brings me to my next point, which is that the examples given above about horribly optimized characters and broken mechanics seem to imply that high-level play is a common part of Adventurer's League. Simulacrum, for instance, is a 7th level spell. In order to cast it, a PC would need to be level 13. Right now (unless I'm missing one) there is exactly 1 DDEX adventure that is playable by a 13th level character. (There are also the Epics, AO and hardbacks, but the number of Tier 3 games in AL must be exceedingly small.) The idea that a level 13 character (who has earned 120,000 xp) might be quite powerful doesn't bother me in the slightest.
And as for the fear that a player might choose to DM for an entire season to game the system and get a character into Tier 3, with great magic items, etc., the math really doesn't work out. Let's assume the worst case scenario - a player who has been DMing for 40 years and who DMed the last 4 seasons of AL (16,000 xp), runs all 14 DDAL adventures *and* Curse of Strahd this season (61,200 xp, assuming they did the LE as well) and even finds time to run DDAL4-1 five times (an extra 10,000 xp for Deja Vu and Teacher of Lost Souls), they would receive a whopping 87,200 xp, putting them at level 11. They would also start off with 4 magic items from Dedicated DM and Agent of the Tarokka and Barovian Noble, a common scroll or potion, an uncommon potion, an uncommon scroll, and a rare potion or scroll.
In the process, they would have spent the entire season (March-July) DMing - far more than 30 sessions for possibly over 100 different players. That seems like a remarkable amount of work for someone to "cheat the system" and get a powerful PC. Presumably, a player who played the same character through DDEX/DDAL material over the course of those five months would end up with a comparable character (or one of even higher power level), and they would have had the fun of playing the game, too.
