I understand that they wanna change the weapons for PVP.. now these days PVP is just trash because of some weapons. But with this decision they also getting obsolete for PVE in the long run. and beleve me.. new weapons will come so we need to grind again for them with new ornaments that we can buy again. and than they take them down again? not on my watch.. i'm out of here if they do that

Not really. They’ll be useless in high level strikes, nightfalls, raids, dungeons, new public events, any new activities they add, IB, and trials. The only place you might use the left behind guns are in regular crucible and maybe gambit if you hate life.