Combining crucible trees - allocating passives seems like a waste of time & very frustrating

Did this twice today trying to get a level 5 node onto another weapon.

Failed both times - there were 7 allocated passives across both weapons. The combined tree got 2 of the tier 1-2 mods and 3 of the unallocated mods.

Seems like a huge waste of time given that it takes about 10-12 t16 maps fully charged to go from lvl 4 to lvl 5.

I'd be much better off just buying a weapon from trade with no nodes allocated and then forge it onto my weapon over & over.