Update:
As I've shared, my level 46 Ranger got shut down hard at Act 3 Cruel. 700 hp & 1200 armor is a weak ass glass cannon where I can't even let them touch me. 700 DPS is obviously not good enough either, takes forever to kill regular mobs.
So I got sick of it and started a total opposite tank Marauder build focusing on everything life & life leech. (after learning Life is the best investment above all)
He's level 37 now, Act 1 of Cruel and already have 1400 HP, and same armor as Ranger already. BUT Flaming Shield gives another 700 armor and Enduring Cry gives me flat +15% armor reduction on top as well as +15% to all resistances.
I distinctly remember having an awful time and Cruel's Fetid Pool with Ranger (get 2 shotted and die). Well this guy can took it like champ. He could even tank Act 2 boss's big FUCK-YOU melee attack, which 1 shots most heroes.
Thanks to Blood Magic (spends life instead of mana), I have absolutely ZERO mana problems. I also lucked out with various lifesteal gear and gem.
So I'm doing whopping 16% lifesteal AND 60hp/sec natural regen (about 3%/sec). This build is so much fun. I hardly touch my flask, and it's super fun to take massive amount of abuse in the middle of the big mob and beat them up. So satisfying compared to the scared Ranger. The best part of this build is that whenever I fight bosses, I can go toe-to-toe and bash their fucking skulls in.
Here's my Marauder Build Passive Tree (so far, I will continue to get those 9~ life nodes all around).
He's a lot of fun. Will provide further updates to see how he fares in Act 3 of Cruel... and even if he can finish the game at Merciless difficulty (build is correct, just need time to get elite gear).