If the sentence replaces Europe with "is the" it would read "Ariane 5 is the most successful launch system to date" That's not remotely true, see Falcon 9 for

If the sentence replaces Europe with "is the" it would read "Ariane 5 is the most successful launch system to date" That's not remotely true, see Falcon 9 for example. 282 successful missions so far and they are now running about 100 launches a year. I'm not trying to put Ariane 5 down, it's great for what it's supposed to accomplish, much like SLS is good for what it is supposed to accomplish. A govt jobs program that occasionally launches stuff into space. If your goal is launch stuff into space as cheaply as possible, they are total failures. If your goal is to create a jobs program and keep the local population capable of launching stuff to space, then they are obviously successful. Just like Ariane 6.