After REVO came out, I managed to land Go Rai once or twice, and
since then, I haven't been able to climb past Sumuje (Lv39) ~ Yongmuje (Lv41) and just hover around there.

Personally, I think that for those at the Maoh level or higher,
there isn't a huge difference in basic skills like combos.

The difference, however, lies in

how well you can squeeze in the maximum guaranteed combo even in tight situations with guaranteed counterattacks
(e.g., Jacky 6PK is -16, so in Shun's case, a Do Wan combo is possible as a guaranteed counterattack)

I think that's the difference...

Or the difference in know-how regarding how well you can appropriately block the opponent's evasion with the fastest throw,
or using throws to prevent the opponent from doing anything stupid in frame advantage situations, or using techniques that don't get countered in advantageous frames)
(e.g., +6 situation, Jacky High Angle Kick 6K)

I think that's about the only difference...
Good luck to everyone who has reached Maoh. Getting to Muje is not difficult.
Staying at Muje is difficult. (Sniff...)