I think the big thing with Acend is not only are they a good team, they player for player match up with SEN effectively. They also definitely have proven to be at the level of a Gambit or SMB even though they got 3rd in challengers finals.
One reason I believe Gambit are not being rated highly is their lack of a superstar duelist, they have Nats and he is great but not the entry. I feel people equate team success with how good your #1 duelist is and for Gambit that can lead to them looking lackluster. Realistically they are a well oiled machine that is very balanced but idk.
SMB is due to how new they are. Also, they can flop the most out of the 3 due to their heavy aim duel playstyle. that will get shut down by SEN as no one can out aim that at this very moment.