Doing some very simple number crunching, I actually think the Investigator probably comes out around average, probably -just- below average actually, on hit chance so long as you have WIS and your "to hit" ability at 16.
If you Take the Case on an enemy, you get to do your Study Suspect for free. By Taking the Case you get a +1 to your perception check to study, effectively the same +1 you would have had if WIS had been 18. As an expert in Perception at level 1 increasing to Legendary, you should statistically be succeeding this check very frequently since it's basically equivalent to a fighters "maxed out" attack roll. (Except against WILL DC instead of AC which in some cases might be better, some worse)
Upon success you get a +1 to your attack, the same +1 you would get if you had 18 instead of 16 STR/DEX. However, you get the added bonus of Studied Strike damage on the attack. Being trained in this attack means you basically have the same "to hit" as most other classes.
Obviously it's not perfect. It's not ideal for a class to have two abilities that MUST be 16 to function normally. Not to mention a dependency on rolls to get those +1s just to reach average "to hit" doesn't feel great.
But I think the out of combat functions and the support functions the investigators bring will feel great. Combat Clue, Detective's Will, and Clue Them All In basically make the Investigator a better support class than the Bard. Thrown in Known Weaknesses to make Recall Knowledge useful again as well and you have a pretty great support character. Knowledge is power after all!