First of all, please guys, start reading the skill description. It was clear from the start that Blind Side is a debuff that applies a chance on critical hits separately from your crit chance:
Use a magnifying glass to find the enemy’s blind side and attack. The attack will apply as critical attack. Foes around the attacked enemy will have higher chances of being hit by critical attacks.
(The effects of Blindside and the character’s critical rate apply separately.)
2nd, if you want to calculate the crit chance of Blindside, it would be very clever to reduce your natural crit chance to 0 by removing all critrate buffs and critrate equipment prior to the test and fight only against monsters who are at your own level or higher than you (so that their crit defence negates all of your natural critrate), best bet would be unequipping your weapons and fighting against a Saalus Boss or Mercenary Mission Boss.
And, to have some “accurate” test result, you have to test for at least 1000 attacks, normally you need a sample size of 10000 for a good average probability test.
First part was already answered by the skill description itself, there is no connection.
Second part is actually the opposite, the more critrate you have via gear, the less additional crits you can get via the Blindside debuff.
This is due to the reason that you can’t crit twice on a hit, so if your critchance makes your hit a crit and blindside debuff triggers on the same hit, it will still be a normal critical hit.
Once your critchance grows, so does inevitably the intersection of natural crits and Blindside debuff crits, making the buff become more and more unimportant.
Basically, depending on the critchance of the debuff and your critchance via equip, at a certain point going Rogue will give you a higher critchance than Appraiser, even if you only have 20-30% chance on backattacks via Werewolf cards.