Although I understand why Marriott matches SPG Gold only to the new Gold status, it feels quite unfair for people in my situation.
In 2017 I had 24 nights (11 stays) with SPG, and 42 nights with Marriott, that's 66 nights in total which would've easily qualified for Plat this year. I had platinum from SPG in 2016 and matched to Marriott plat in 2017. I decided to explore brands on both sides in 2017, and towards end of the year I had a choice to achieve Gold either through SPG or Marriott. I decided to qualify with SPG by stay just because I liked the Westin slightly better than the Marriott in the same city, knowing that it will be matched anyway. Had I known the new rules last year I'd definitely make a different choice.
What made me even more disappointed is that I already booked my summer vacation in August (some nights with Marriott), even before the new program was announced. Marriott is really messing up people's plan this time.