I know a lot of people are running Gamma Burst like you are, but I have had success on the Takedown running only the Hunter and Stalker tree and swapping between the Rakks and Fade Away. Fade Away for the more powerful enemies, Rakks for the general mobs. I use a shield with apply terror on ASE, a grenade with health regen while affected by terror, and weapons with either 100% damage after an enemy is hit by Rakks or other favorable elemental or terror anointments. This allows you to skip some of the heath regen skills that Fl4k has, which are not that great, and focus on DPS skills.
I actually find that you can grab either Megavore or The Power Inside and be equally effective. Just my 2 cents though, I know a lot of people really like Gamma Burst and that tree.
To be fair though, I have yet to kill Wotan solo on M3. I can get there no problem, but he is a pain to kill. I have gotten past the first two stages, but that third stage (I think it is the third stage, maybe the 4th?) where he spilts into the bottom and flying top is just really tough to do solo for me. I will get there, I guess. Or not LOL.
EDIT: I use the Cosmic Stalker COM, with +3 to Interplanetary Stalker and +2 to Hunter’s Eye. I got lucky on the passives, +25% weapon damage and +5 grenades. Then I use an artifact that has bonuses to cooldown, magazine size, and shield recharge delay. I alternate between the Stop-Gap and the Re-Charger for shields. Whispering Ice, Hunter-Seeker, and Hex for grenades.