This does feel very focused on damage test results in general and I'd imagine in the interceding 4 years SGM coming around to view tanking as the easiest way to approach the game would shift values here a decent amount. Most notable is that Flinx Fur Coat gives 1 defense, while competing chest pieces give 5 or 6 defense and potential set bonuses. Not even gladiator or shadow armor here, but gold/platinum armor, fossil armor, jungle armor, armor sets where the piece is comparable to what you need for flinx armor anyways.
If the tier list was actually biased for damage tests or otherwise max DPS, then Blade Staff would drop down to A, Forbidden Armor would rise to A, Tiki armor would drop to A and so on.
The thing with defense is that the gap in defense from Summoner armor to Mage/Ranger armor doesn't really matter much. Having more (or lacking) Max HP, health regen, i-frames and so on makes a bigger difference to survivability. If I was playing Summoner and had to pick between Cross Necklace or +30 defense with no drawbacks/conditions, I'd pick Cross Necklace every time. Mostly with Melee armor, mainly w/ Warding, does Defense start being a huge contribution to survivability. Not to mention that having more minions is better for crowd control in general.
This one is admittedly very anecdotal, but I found myself surprised by how not amazing flinx snapthorn was against Skeletron and how workable spider staff was against Twins. I wouldn't say spider staff is easier against Twins than flinx snapthorn is against Skeletron, but it wasn't harder by much in my experience; I just needed to be cognizant of Spazmatism's second phase due to my lack of range, but spiders actually did very well with attaching between dashes due to Spazmatism's low speed then.
Unless you meant only Flinx as the minion, Flinx mixed with other minions performs very well against Skeletron. Not the #1 fastest or even easiest Skeletron setup, but still very much competent with Flinx being a significant contributor.
Spider Staff just mostly doesn't work well against Twins since Spider Staff's higher raw DPS is greatly undermined if not invalidated by the fact it won't be hitting the twins really consistently. Maybe there's a world where three spiders mixed with Sanguine Staff has slightly higher overall damage output if you play more aggressively, but I don't think this is really something worth mentioning or taking into account in this case.
I also don't understand the Shield of Cthulhu mention. Why use it in hardmode? [...]
Instant acceleration, which besides being generally useful for dodging attacks and escaping bad positions, also lets you max out Unicorn mount's speed instantly. Particularly useful for making dodging phase 2 Spazmatism easier.
It has its flaws, but not for the reasons other people say.
In other news, I decided to drop Finch Staff from A to A- because looking back on it, I found myself overhyping it a bit considering much of what I talked about didn't really end up being something I took advantage of at all (Rushing shimmer for Finch, and also its piercing on evil bosses, even Flinx + Snapthorn is good and fast enough to the point considering using Finch instead isn't very important or massively impactful). I also changed the description a bit.