While it's true that Koth is strong again thanks to all the mono-color gem changers available in standard right now, I still find him wildly inconsistent in actual gameplay. Sometimes you steamroll him, sometimes he has a ridiculous boardstate by turn 3. Hard to treat him as a top-tier candidate in PvP events because there are much more reliable walkers in dual-color red(and of course Bolas).
What balances Samut out is her extremely restricted deck capabilities. If she had one more spell or support capability in her deck, she'd be in OP territory for me. Again, HUF is broken, not Samut. She is a great walker, and I use her a lot, but yea it's very dependent on HUF and HoD's strength.
See, I don't agree that his mana bonuses are overpowered. I've used him enough to understand the limitations of his mana loadout. I thought his mana gains would be far superior to DB, but the -2 on black really hoses a lot of would-be good matches. And DB's first ability is far superior in practice to Teferi's. His 2nd and 3rd abilities are great though, I do agree. In the end though, his mana gains end up on par with DB a lot of the time.
Again, the culprit is one glaring card in blue, not the planeswalker itself. He does happen to be the PW who benefits the most from vault due to generating his own tokens, but if it's ever fixed he will be balanced again. Also, his lack of cheap support destruction balances him out especially in the current meta. Many games come down to who gets Vault out first.
Vraska is a very mediocre PW without her first ability, which is her saving grace. In fact without it, she is 'underpowered' territory. Her mana gains are average, her other abilities are OK, and her color combo is great yet she still tends to fall short of other dual-color walkers who have green and black as other colors. Her first ability right now is currently bugged anyway. We shall see if new sets make B/G a more viable combo for standard but right now she is low tier-2 for me.
I'm trying to use posts like this and others to help guide which PW to get next, but I'm having trouble reading your rankings. Who is Jace 2, Lilliana 3, etc ? I gather its the order they came out? but that doesn't seem to be easily discoverable in game. Is there an easy to reference list somewhere?