Any chance you just got super unlucky with your d20 perception checks? Every char makes a perception check separately from my understanding, hence why you let all your team mates walk side by side instead of running ahead.
Overall I agree that cones of perspective should be made larger as your trickery / stealth stat increase. I would be more then happy with a detect trap magical ability [cantrip]. And maybe a spell to disable all detected magic traps. Would make the under dark a lot less annoying to navigate
