are pendulums unbeatable in the advanced format?

Pendulum isn't unbeatable. In fact, from what it used to be, pendulum decks (namley decks comprised of Performapals and Dracoslayers) are heavily nurtured (but still very much playable.)

You have multiple "techs" out there to stop your opponent from pendulum summoning. Some of which people have already listed.

The key thing you want to do is either knock out their pendulum scales preventing them from summoning monsters (Mst, twin twister etc.) or simply lock them out from summoning at all with flood gates (Anti-Spell Fragrance.)

Pendulum decks are not the only decks in the meta. The most popular decks prior to the Banlist were Monarch and Burning Abyss Phantom Knights (dubbed Pk Fire). Neither of which used the pendulum mechanic.

Blue-Eyes, which recently got new support, is also expected to be a very good deck which does not use the pendulum mechanic.

Keep in mind Pendulum decks comprise of multiple archetypes. Some pendulum decks even struggle against decks which do no use the pendulum mechanic at all.

/r/yugioh Thread