I have to agree regarding the loss of profit, I was in the same boat, had armstech, scavenging and underworld trading until level 45, when I realised to make any epic gear at 50 I will start needing special mats, by this point I already have 400 Underworld trading and was sending 3-4 companions out at a time to get Companion Gifts and selling them for profit. Aswell as all the other rare materials that I could sell for profit as I wasn't using them.
After dropping Underworld it took me 2 days to get Investigation back up to an acceptable level, now have it at 400 and I only ever seem to get 2 Companion Gifts missions at a time for level 49-50, sucks compared to Underworld trading imo.