In Twilight's Kingdom we had a fight scene with Tirek where they both wielded kamehamehas and all that other Dragon Ball Z stuff. This is a huge step up from Nightmare Moon who literally just stood there and monologued while Twilight figured out how to defeat her.
Then we had Discord who wanted to turn the world into chaos, and actually started to make some progress but completely underestimated the Elements of Harmony.
Then we had Queen Chrysalis who while wasn't very original with her attempt for world domination (I haven't watched A Canterlot Wedding in a long time, plz don't sue me if I'm wrong), managed to actually defeat Princess Celestia in a battle and her army stopped the Mane 6 from retrieving the OP elements of harmony (volvo plz nerf) thus knowing of their power.
While King Sombra's a really shallow character, he does not monologue, uses dark magic and sticks to his priorities. His only goal is to steal the crystal heart, nothing more. Also, did they actually KILL Sombra in the end? We saw him literally blow to bits, so he might well have died.
Tirek literally sucked the power out of all the ponies, the spirit of Chaos it's self and 4 alicorns, and tricked Discord to betray the Mane 6, thus upsetting Fluttershy (now that is truly evil), followed by a Dragon Ball Z style battle and the even more OP rainbow power to defeat him (-No random critical hits).
So God knows how ridiculously OP the villains get in future, next thing you know, they'll be battling in outer space with power levels over 9,000,000,000 and even the power of friendship struggling to cope and casually blowing up entire planets like it was nothing.