The tiger gets to insane levels of evasion if he roars enough and his level ups are not reset. It does not have to do with accuracy. That is why a RNG setup is not ideal for Vidala. You want either a SCH making wind chains for other mages to burst or you want DDs capable of light with mages to burst wind. It is not a fight that can be done without mage support.
Untrue. Not that it's the norm but I've done it as PLD + THF + BST and as GEO + BST + someone AFK in the corner.
I will say that skillchain + MB is definitely preferable, or just a full mage setup, but the only trick to killing Vidala is killspeed. You never need to proc him, you never need to SC him, you never need to silence him (though it helps), you just need to make him not be alive anymore before he roars too much. However you choose to do that is fine, provided it works.
The problem RNG, and really all DD (mage and melee alike), have in Escha is 100% due to it being higher level content than people are used to. The evasion some of these NMs have is such that it makes AA MR Very Difficult look like a fight that you could eat meat on. Most DD do NOT currently have the gear to effectively fight these NMs without GEO/COR/BRD buffs at all times.
Rule of thumb for ACC before any debuffs (distract/frazzle/torpor/feint/etc)
T1: 1050 (Vidala / Gulltop 1100+)
T2: 1050~1150
T3: 1400+ (this is not a joke)
tl;dr: level GEO or tell someone you trust to level GEO if you want to do Escha. Torpor and Frailty or Malaise and Languor are your friends.
My group has cleared every NM in Escha as BSTx3 GEOx2 COR (except rabbit as BSTx2 PLD GEOx2 COR). We farm T3 in batches of 6~10 pops per kill since update as PLD WHM BSTx2 COR GEO. More than one way to skin a cat, obviously. I think PLD SCH BLM GEO setup is a lot more foolproof and requires less specific gearing. Your mileage may vary.
Edit Re: TH
Either accessory or armor is 100% drop from all T1. With sufficient TH and luck, double drops are possible. It's worth your while to bring one if you can.
T2 have 100% drop rate on either a weapon or accessory, same as T1.
T3 have 100% drop rate on 1x Eschalixir +2, anything beyond that is TH based. Pulse armor/weapons are (not a joke) VW drop rate with TH or without. There is only 1 confirmed Pulse body across all servers, most farm groups have seen 0~2 weapons total. My group is 1/200+ weapon-dropping T3s for weapon, and our only drop (lance) was without a THF.
THF drastically increases chance or Vulcanite Ore / double drop on +2 though.