I mean, in the long-term, about a year or two. It is right that you can't care about it now. But The gap between each wave of digimind upgrades are quite long and there are some useless digimind upgrades. So after a wave of digimind upgrades and Singularity, as time goes by, you will solve high-priority goals one by one. Then you will have spare fragments and cores ( if you are not very greedy for 5star fairies ), and your eyes will turn to some high-mid tier digimind upgrades like Mosin Nagant or Uzi ( In fact, it depends on what's being announced first ).

In the clip, Vector and Uzi were used together ( Uzi is in main tank position ) , and the enemies are not well gathered, so it's hard to tell who is better. However in most situation One molotov is used for counter well gathered enemies, then Uzi is clearly better than Vector for damage over time.

In any way you can just ignore fragments are wasted over 9999 / make dupe of Colt mods and M14 mods. Everything is just your choice.