As a Shen main myself, as much as I hate to admit it, Shen DOES NOT need a buff. Op.gg and Lolalytics has him sitting at a 49.1 - 49.8% win rate. For a champion balanced purely around professional play and team coordination, that's pretty damn good.
Yes, he's just an ok pick in top lane. Is he great? No. But is he bad? Also no. You're not meant to be a carry in the sense of blowing up your opponents in 0.3 seconds. THAT'S NOT YOUR JOB. Your job title is "Warden". You are the bulwark, the frontline, the protector. YOUR JOB is to keep your teammates safe so that they can blow up your enemies for you.
You have all the tools you need. A gap closer, that is also an escape, that is also a multi-man cc, that is also an engage tool, that is also a peel tool. You have an AOE auto attack dodge, that can absorb infinite damage for 1.5 seconds from auto attacks. And most importantly, your ultimate. A global shield that also teleports you to an ally in need. These things have high cooldowns because they have to. Proper usage and respect for your abilities wins games. Failure to recognize just how powerful your abilities are and using them willy-nilly loses games. Timing is key.
YOUR WIN CONDITION IN LANE is to not feed. Doesn't matter if you never kill your lane opponent. True damage doesn't matter if you never die in the first place. Hug your tower if you have to, JUST DON'T DIE. Go even. Watch the map. Keep a clear eye out for ultimate plays. Be the game changer. Turn a 1 vs 1 into a 2 vs 1. Turn a 2 vs 2 into a 2 vs 3. A single ult is the pendulum that can shift the scales into your team's, or the enemies.
And if you lose a game? Fine. Whatever. Remember the old saying. 30% of games are impossible to lose, your teammates are so good its decided for you. 30% of games are impossible to win, your teammates are so bad its decided for you. 40% of games however, that's on you to decide. Maybe you've have too much of the first category. But I can assure you, for the last one, I would gladly pick Shen every time.