The No.1 rule for keeping games fun and balanced!
Great to hear you've found yourself a fun group that keeps the proper 40K ruleset alive. I've concocted my own 6th mini-group among my family members that play Warhammer and a couple of friends that uses 6th Edition books for the armies that have them, and 7th Edition books for the armies that didn't get 6th ones (ignoring all the crap like Tactical Objectives and formations that 7th shoved in).
Yeah, the only real problem with 6th (that continued in 7th) was that Tau and Eldar were just made so strong (though the ultimate undercosted dick unit that was/is the Wraithknight certainly contributed a lot to that). I notice how even today there are sites like 1d4/1d6Chan that give the Tyranid 6th Edition Codex flak, but to be honest, especially with the added 7th units like Tyrannocytes and Toxicrenes, I still think it's solid against most armies - Space Marines of both flavours, Daemons, Guard, Orks, even Necrons if you disregard the formations, are all fair game for Tyranids, it's simply that the Tau and Eldar books raised the bar so high powerwise that anything that everyone was hoping/expecting the Tyranid book to follow in the footsteps of those two, when of course instead it chose to join the Chaos Marine and Space Marine ones in being a lot less cheesy.