I rarely ran into Landorus, and I even used a Landorus team for my first run but overall, I think it is very good but not ban-worthy. It effectively checks common threats like Amoonguss, Diancie, Heatran, Incineroar, Volcanion and Zeraora thanks to its tremendous power and coverage. As such, it is hard to predict which Pokemon can be a safe switchin to Landorus. However, it is checked by the two most common Pokemon in the tier: Kyurem-Black and Rillaboom. Additionally, other priority users, weather abusers and generally faster attackers can quickly finish off Landorus. In combination with the abundance of Ice-type coverage and its underwhelming bulk, Landorus is usually on the field for a short period of time. Ultimately, it is still a top-tier offensive threat, but its vulnerability to a variety of common checks makes it not really ban-worthy.
During my second run (this alt), I was inspired by Tornadus in 2v2 and used
NotlPrimRose 's Rain team and it was great against the ladder. Prankster Tailwind + powerful attackers + Beast Boost make Landorus no problem for this team.
https://pokepast.es/559c6ebe5344dc56