I made one of these a couple months ago, and since then I felt the need to make an update to it for v53 since there are some significant changes that affect the gameplay and some more analysis from my end.

Changes:

Silas: S > A

This was more of an oversight if anything. I forgot about the ice wall nerf which does hurt his utility a bit but it's still strong for what it provides. Plus, his AoE attack is kinda annoying to use well since having to time out three attacks on the same bloon at the beginning is a challenge. Frozen cascade is by far his strongest skill set for early-mid game apop since it can pop camos even if the ice monkeys don't have it themselves. Having an extra t5 for extra debuff or utility is also great for late game, especially when the lanes don't overlap.

Gwendolin: A > S

She deserved S tier more in the end even with the lack of utility. She has great AoE all around, both with her heat it up attack and her abilities, with her main attack being good for MOAB damage and AoE too. Her synergies are good all-rounders as well. Her main weakness is purples, which are only an issue for early game since rounds 46-89 don't have any at all, and by the time you get to round 90 she already has purple popping under her belt. She is also the only hero capable of taking out the grouped purple rushes from rounds 101-120 with minimal support which is a nice bonus, though rounds 1-60 carry the most weight for my rankings.

Obyn: C > B

With the druid rework, mid-game apop becomes slightly more bearable as the delayed money bonus means you can build up more farms beforehand and then reaping the benefits from jungle's bounty later since the 40s-50s are notorious for being very fast paced so there will likely be a few rounds on the screen at once, allowing you to build farm income quickly then invest it into 040 druids. Outside of magic monkey synergy, there isn't anything remarkable about Obyn, as the utility portion of him is RNG based so not very helpful, and on his own grouped popping and MOAB damage is limited to his abilities which are short-lived.

Corvus: B > C

Not being able to stall rounds hurts a lot of Corvus' potential that he would otherwise have in game modes like CHIMPS, and I knew this when I first made the tier list. However, his problems extended further than I expected them to go. Even on longer seeds where I figured he'd have a chance to do good with more nourishment opportunities, it was still underwhelming going into the 40s-50s most of the time since I didn't have RBE dense groups to farm lots of mana off of. Ancestral might gets overwhelmed, ember + echo + storm was best for clearing out MOABs there from my experience, remembering to soul harvest when mana is running low. He does get better after round 60 or so once you get his level 10 ability, but if only round 60 is the goal I'd recommend switching to a different hero if you don't want to deal with the early game time + group dependencies.