The old system was more of a combination of pure luck and fights with others.
The new system allows players to get it via various methods which overall stimulate better teamplay.
Pure damage output doesn't always mean a lot, you could farm a lot of damage off the same team, getting a lot of evo points.
With the current system a bit more is required than just that, and if you can't find a proper fight to engage in, you won't be at the mercy of the RNG shield spawns.
The current system is also a bit more streamlined in such a way that there aren't any major differences between shield levels, which was entirely possible with the previous system.
Can't go for fights in some cases? Plenty of passive ways to get it, otherwise you can do plenty in fights with others.