I like how Deke phrased it on the Beyond the Data blog.  

"I like to think of long-term change, the kind that has been going on since the early-to-mid 20th century, as riding up an escalator. Transitory bumps from factors like El Nino, are like jumping up and down while you’re on the escalator. "

https://www.climate.gov/news-features/blogs/beyond-data/beyond-2016-year-review

Here's another nice graphic showing ENSO superimposed on global surface temperature data:

https://www.climate.gov/news-features/blogs/beyond-data/how-will-el-niño-affect-2015’s-placement-among-warmest-years-record

So, La Nina may help contribute to a small downtick in GMST, but you're right that we're very globally very warm despite having a La Nina.