She's far too reliant on landing her knock up for picks, but any amount of mobility at all renders her useless with how slow she is, just get kited way too easily and you get stupidly reliant on flash. Please riot, this champ needs something to help her out even if its like moving towrards marked targets increase MS by X% so that landing her Q is more rewarding.
It's all about successfully utilizing your tunnels for flanks. There is no wall you can't clear with a good tunnel, use that.
In my opinion, the place where a small change could make Rek'Sai a lot more playable is in her ult. It's perfect as it is right now, just make it so that it can't be completely dodged with a blink ability. You can ult someone, but if they flash right as you would pounce and land on them, or ezreal E, or literally anything like that, the damage "misses". I think making this not the case would be fully sufficient to put her in a better spot. Plus, lots of abilities don't allow you to flash their damage (in fact most don't...), so it seems weird to make Rek'Sai's ult one of the select few that do.
I agree that rek'sai needs help, but she doesn't really need it in this area. You shouldn't have too much of a problem closing in on and sticking to targets with tunnels + 
Used to be a Rek'Sai main till jungle changes s7 He's fine in a high elo ssituation where there's actual coordination in diving etc. But in low elo its awful, you set up a dive people ping you telling you that turret does damage and to back off
I am a long time Rek'Sai main with a high win rate. I recently have been losing more games, and I feel that she needs a buff now. I think her kit is actually perfect. She simply needs minor buffs to some of the following: defense, damage, attack speed, or movement speed.
Though missing your ult by a flash, blink or dash can be frustrating, I think it's a fair trade for how powerful her ult is. A tip on her ult: Don't use it unless you need to. Rek'Sai has a lot of combat strength (well, until recently) and will generally force the enemy to flash away. At this point is when you ult. It's very rare that I deal with a situation is which an enemy is able to dodge my ult.
