Have you played league much? There are plenty of times where only poking will occur and you won't get to auto much. Think when you are helping your team siege a tower or deal with a siege. You might get off a few autos against some creeps, that is if the rest of the team doesn't have much clear. Or think about when the two teams are dancing around dragon or baron trying to find the right time to engage. You won't be auto attacking much then.
Wait, you know where Rek Sai will probably place tunnels. That coupled with some decent vision will allow you to have a pretty good idea where a tunnel most likely is. If Rek Sai gets behind and her team starts getting pushed, it becomes significantly more difficult to place effective tunnels. It gets even worse if they control your jungle and start placing wards in it.
Her gapcloser is on a relatively long cooldown AND she must be burrowed to use it (unless the tunnel already exists). On top of that, she MUST be in melee range to knock up, and the full knock up radius is very small around her. Rek Sai does not have ranged CC any more than Irelia (Q + E) or Xin (E alone or E + Q).
You need to educate yourself before making claims. Rek Sai's tunneling ability starts with a cooldown of 20 seconds at rank 1 and scales down to 18 at rank 5. Heck, even in URF mode with 80% CDR that would only be a 3.6 second CD. Since you brought up Xin and irelia, lets take a look at their dashes. Xin starts at a 14 second CD and goes down to 10, Irelia starts at 14 again, and goes down to 6. However, Rek doesn't NEED a target to dash to. So lets compare her dash to Ez, Liss and Gnar. Ez starts at 19 seconds, scales down to 11. Liss starts at 24, scales down to 12. Gnar (in both forms) starts at 18 seconds and scales down to 12. So after this quick comparison of non-targeted dashes, its easy to see that Rek Sai's is really nothing impressive. Also remember that Rek'Sai MUST be burrowed if she wants to make a new tunnel.
Noc really isn't in a good place. His damage is ok, but not good enough to justify having him on a team. Outside of his damage, he has a fear, vision denial and the ability to block a spell. Noc had plenty of times he was strong, but those were the days where he had a lot more damage than he does now. Noc, Shyv, Rek, Jax and even Rengar are some examples of champs that without damage honestly bring very little to the team compared to others like Lee or J4.