Software is easier to copy and replace than many other things, but make no mistake: The amount of engineering done at the largest software companies is massive, and has gone way past the point of being easy to replicate. Let's talk someone smaller, like Twitter. Building a Twitter for 100 people is trivial. Scaling it to work well for serious volumes, building all the pieces that make it have actual revenue, and not be just a giant money pit, and all the effort required to build the userbase itself is just enormous. When we go past Twitter, and we think Facebook and Google, serious disruption of their core businesses is really, really hard, because every single user they have is an efficiency you don't.
In practice, every large software company today is running a whole lot of machine learning under the hood. Whether it's figuring out which ads to send you, just get you to stay on the site longer, or just have great fraud protection, the difference in data matters. Imagine your machine learning model is trying to sell ads. How much of a disadvantage are you in vs a company that is the user's default search engine, and has analytics hooks in the websites that your target person is on 75% of the time? What if they also have their text messages, know their friends, and their friends' purchases? You can have much better algorithms, but they have such an insane data advantage that you have to be orders of magnitude better to even compete with them!
So I'd definitely bet highly on those services, because they've spent years building moats. That doesn't mean they are unbeatable: We all remember the time when Microsoft and IBM looked unbeatable, and we all know what happened, but I don't think anyone without massive funding and a completely new, must have product has a prayer of entering their space and not be swallowed whole.
