That's certainly one perspective, the other is that in the consumer segment churn is high but also the are a tremendous amount of people.
Dropbox had a head start but over time other companies like Google where able to build out competing services and because the total population of potential consumers continued to increase, a lead today, doesn't guarantee a lead tomorrow.
The other side of is that what made Dropbox amazing at the beginning, the ability to sync files with direct access on your computer, is actually now a detriment. Many users don't want the files locally, download speeds have increased dramatically (I have 1Gbps fiber at my apartment), so having the files locally is actually annoying and takes up diskspace, so you have a bit of a late mover advantage, especially if the population of available consumers continues to increase.
In this case it isn't simply X couldn't compete with big Tech, the landscape did shift a bit.
It's also important to note that Dropbox is still a very successful company, and if they aren't chasing revenue growth and profit they still provide a great service to consumers. But their growth chasing leads to a degraded user experience, which also pushes people away from their product and has them explore alternatives to really see if it's an apples to apples comparison. And that's where the "cloud" first storage solutions today present a better platform.
What really slows this down is the cost of switching for older customers that have a tremendous amount of data already in Dropbox and have it integrated into their workflows so it really isn't a fun project to migrate off.
This is also where the price increases create revenue growth because customers aren't willing to go through the pain of migration, but you aren't delivering more value to them, instead you are playing off of the cost switching to drive revenue growth and that begins a downward trajectory.