Abyss solo on Titan is easy. Throw on shoulder charge, transmugation, agility, and catapult. Get a running start and x3 catapult into the darkness. Should get you about halfway before the first darkness hits. Knee a thrall in the face who spawns in front of you and it restores you to full health. Plant a lightning grenade directly on the lamp in front of you right before you reach it. Stay in the blast radius of the lightning grenade. Make sure you have aftershocks equipped. Your weight of darkness should be removed right before the Lightning grenade is exhausted. Jump on top of the pillar and use your primary weapon of choice (suggested Fatebringer) to kill as many Thralls as possible. Your goal is to super energy farm as much as possible before the lamp is about to blow and your forced to jump to the next lamp. Super should be ready every 2 lamps, with lightning blowing the behind horde away, and on top of lamp mob farming. Try saving super for Knights and emergency situations.

Proof of warlock solo? Why? If a titan can solo it, then a warlock can easily and I have myself solo'd it. If you put bloom on, your melee and grenade will wipe a group. A vortex grenade will keep you safe if you stand in it. Abuse MIDA multitool speed. Abuse jumping on rocks and blink at 0 Weight of Darkness. It's not really impressive. Not to mention the new Light explosion catapult nonsense. Edit: as for the question, templar is hardest simply because it takes the most time. All the other are doable relatively quickly and don't have any parts that are reallly difficult.

Solo crota bridge as a titan isn't hard

None, since all it takes is practice and basic gaming knowledge. And 99% of the people soloing are using the gjallahorn which makes the solo attempt invalid imho.