There is no way in hell Burgess is pushing Sabo to high difficulty. The mera mera no mi didn't make that big of a difference where Sabo is going from high diffing one character to low diffing the same character.
@Thread
He would beat Luffy and Zoro both with or without the fruit around mid to mid-high (Luffy - Flare fruit) difficulty.
Sorry couldn't reply before(not near a computer)
I think so because before the mera it didn't seem like Sabo could easily beat Burgess in the tournament. The moment he entered the ring, he seemed concern about Burgess(the only thing that concerned him). When they clashed, he barely won the haki clash and ended in a standstill position after their respective named attacks. Later on he had his hands so full with Burgess that he couldn't even protect Rebecca from Diamante(sending Bartolomeo for that) and had to use Burgess' attacks(weakening the coloseum floors) to take advantage of and steal the fruit. Even after gaining the mera and growing accustomed to it, he still said he can't protect Luffy while fighting Burgess at the same time, probably due to his past knowledge from the coloseum and eventhough he ended up low diffing Burgess, it still took him more than 10minutes to do so and he had no reasons to hold back with Luffy in danger
And this is considering that i do think he gained a lot with the mera
1- He gained range destructive attacks
2- He gained logia defense
3- He gained maneuvrability
4- He gained much destructive dragon fire moves
He used all this things during his first engagement with Burgess, dodging his attack with intangibility while following up with a much stronger version of dragon claw(fire dragon claw) which was city busting attack as opposed to his regular dragon claw that wasn't even close to be that powerful
It seems that pre-mera Sabo had the agility and haki advantage when Burgess had durability advantage and even the gap in their close combat skills weren't big enough for Sabo to completely overwhelm him. Considering that he took the initial flame dragon claw with minimal damage, and that it took him more than 10minutes with range destructive attacks and maneuvrability advantage to put him down, it will take even much more than that for pre-mera Sabo's attacks to affect Burgess especially since it will be harder for him to land in close combat without range, without being in danger himself
Under these conditions i think it was heavily implied that Burgess wasn't that far off from his level before the mera. Sabo was portrayed stronger, but not with enough gap that i think it would have been mid diff