>>57803511First, it's always been portrayed as physically attacking using its arm blades. This is seen directly in the anime and consistently referenced in Pokedex entries.
Additionally, Leaf BLADE was its signature move in Gen 3. The reason why Sceptile has a higher Special Attack stat was because all Grass-type moves were special moves. When types were no longer locked to physical or special in Gen 4, Leaf Blade became physical, whereas Sceptile's stats remained the same, leaning into Special Attack.
Now, let's look at its current Gen IX movepool.
>SpecialSceptile learns about 17 special attacks, spread across only 4 types
Sceptile also does NOT learn any status moves that bolster its Special Attack stat
>PhysicalSceptile learns about 46 physical attacks, spread across 10 types
Sceptile also learns several status moves that bolster its Attack stat
Sceptile is designed 100% to be a PHYSICAL attacker. But the half-baked physical/special split in Gen 3 screwed over its stats, seemingly permanently.
IMO the only way to resolve this is to replace Unburden with an ability does one of the following, like
>>57808479>Turns all physical moves into special moves>Allows all moves, physical and special, to use its Special Attack stat>Brings up its Attack stat to match its Special Attack stat, like a free stat boost 
