Masterwork cores drop very frequently from many sources now - vendors, rank ups, deleting weapons / armour etc. Its not hard to get 10 quickly to convert to a prism. Prisms drop fairly regularly from Crucible when you have the mod on the ghost for precision kills. I generally get about 3 or 4 in a few hours session. Its easier than ever to obtain cores / prisms / shards. I started this season with no masterworked armour and only a few prisms and masterwork cores. I have never bothered at all masterworking to the top level any armour previously and never had a shard on my inventory. I now have every armour piece masterworked and 6 shards in the bank ready to go. That isnt through playing that much either - maybe 10 hrs per week. I dont really PvE apart from doing the bounties from the gunsmith each time im on and just crucible for the rest.