They are completely viable. I went mining yesterday for a while in my gunless/shieldless T7. Dropped into pristine metallic ring, boost till clear of radar targets. Mine away blissfully. Cargo is full head back. Get interdicted, immediately boost, pop chaff, boost, low wake out, land profit. He wanted to try and interdict me again but I wouldn't let him. The interdictor has to be behind you, if you tack back and forth toward your target the NPC will never get behind you, if you just fly in a straight line will. So that particular NPC mucked about and followed me while I flew back, dropped into the station with me where the system authorities and Coriolis station promptly blew him apart while I docked and had a beer.