I use straps on all my deadlift training, and just recently pulled 585 without straps at a bodyweight of 191.
It's silly to let your grip limit how much you pull in your training. I use straps so that I can focus on my form and technique while I blast the weight rather than worrying about losing my grip. It also allows me to pull double overhand, which reduces my risk of trying to "curl" the weight and tearing my bicep. I use CoC grippers to train my grip, and can close the 2.5 with either hand.
Train your grip to get a stronger grip, and train your deadlift to get a stronger deadlift. If you can pull the same with straps as without, then more power to you, but if you can pull more with straps, pull more.