Megawatt's hitbox does start at the same frame as Dragon and Ramram*. So it's deceptive like that. Megawatt does have the added advantage of not having a big blindspot due to its size (RamRam's blindspot is diagonally above her, Dragon's blindspot is a bit wider because it lacks the ring's coverage). The blind spot thing is due to the hitboxes being on the fists / weapons rather than the arms. The trait shared by all three ARMS is the high end lag - it takes roughly 1/2 of a second for the ARM to come back,
As for Megawatt being deceptive, it can also beat spotdodges:
View attachment 277014
Should also warn Min Min players to play very carefully around
: she's the main exception to the "ARMS attacks are not affected by counters" rule:
View attachment 277013
That's not the only reason Bayo's very dangerous for Min Min (her bullets and off-stage combos can be hellish for her), but main point still stands. Most counters are safe for Min Min, Bayo's and Incin's are the exceptions.
*(The ARMS attacks come out on Frame 14, aka. almost 1/4 of a second. Aerial ARMS attacks are Frame 16. Neutral Air is Frame 8 for Ramram, Frame 10 for Dragon and Frame 14 for Megawatt. Not counting the buffer or online.)