Vaibhav5viv: No one tiers up "early" due to MP and credit wins.
With the reservation that these subjects have not been clarified to the bottom:
Both ain't true, AFAIK.
With the former (match play), players get a substantial reduction in average and they may apparently slip through the tiers without ranked play.. But, this effect seems to vanish with the number of wins.
With the latter (credit wins), players get a massive reduction in average AND a reduction in ranked rounds necessary. They may tier up prematurely.
And credit wins means all credits won in the game: in tournaments, RGs, Brackets, as well es winnings in challenge MP games. So, when a TM beats a Legend in a challenge match, it will give him a double push.
Disclaimer: Don't know about the typical mobile games.