Can Billie Eilish's success be compared with Lady Gaga?

I mean Lady Gaga was still popular for like the majority of the early 2010’s so it depends if Billie Eilish will stay popular for the majority of the early 2020’s.

hell no LMAO

Not even close, also I will have to say I first saw Billie Ellish on that MTV TRL reboot that failed in 2017 and came out of the gate with no splash
with her first single. Was not until late last year advertisements for her started ramping up with her new album, the label payed tons of money
for radio spins and Rolling Stone placement in 2019.

She is not even on the level of a Kesha or Adele, by the time 2009 rolled around everyone knew who Gaga was, elders, kids, 40 year olds,
show someone Billie Ellish's pic and you prob won't get as many people who recognize her.

Maybe not to the exact same extent as Gaga, but I'd argue that she is the biggest household name out of all the new artists to have debuted this year. How many people over the age of 35 would know who Lil Nas X or Lewis Capaldi is? Billie Eilish has definitely cemented herself as the biggest defining artist of the current Top-40 music scene and the fact that she does have a huge following with the 35+ crowd sets her apart from her contemporaries in that regard. I mean, the "Dad Guy" meme on YouTube a few months ago became viral and attracted millions of views. You've even had popular figures such as Dave Grohl who have come out and spoken positively about her image/music. These things have made headlines in the mainstream. The truth is, you're always going to encounter some people (whether they are young, middle-aged or elderly) who are absolutely out of the loop with what's going on in Top-40 music, regardless of the amount of fame an artist has achieved. 

In any case, I think it would be near impossible for any artist to reach the level of universal pop stardom that Gaga achieved over eleven years ago, given how the media and society in general have become so much more fragmented since 2008. That is only going to exasperate the amount of people who are not in touch with current trends in music. In a hypothetical scenario where electropop was the "in thing" at the moment and Gaga had only just debuted onto the charts early this year, I doubt her mass stardom and influence would be too dissimilar to what Billie Eilish has experienced with her minimalist, alt-pop aesthetic in reality. Billie Eilish is the "Gaga of 2019" when it comes to how resonant her music has been in the streaming, social-media obsessed world that we are living in today.

Artists such as Lady Gaga, Katy Perry, etc. that became popular in the late '00s I feel are the last of their kind.
What I mean by this is I feel in the long run they will be the last to ever reach the level of popularity of artists such as Madonna and Cyndi Lauper.
They were the last bunch of artists to become popular before music streaming services became standard, to become popular through radio airplane and television alone.
As much as I dislike them, their songs were iconic and presentable enough so that everyone and their grandmother recognized their music when they heard it.
With new artists such as Billie Eilish, Aleissa Cara, etc., much of their fanbase prefers to listen to them on apps such as Spotify, Apple Music, and YouTube, rather than on the radio, therefore the interest is now into making viral web hits that will only have a flash of popularity before fading away into obscurity rather than making memorable radio hits. This is why songs from even the early part of this year are for the most part irrelevant already, while hits from the '80s, '90s, and '00s are still relevant to this day.