Translations of the dev's additional comments via FFXIV Subreddit Discord:
"About 13% of the quests we completely took away, but there are a lot of quests that introduce NPCs that are reappearing in the later story, so those had to stay. BUT we took away a lot of the steps in those quests that are required to complete them"
"So you will be completing these a lot faster now"
"So less quests and the ones that remained got easier to complete"
Y "A lot of players get stuck in this part of ARR and then quit the game"
"Surprisingly most players that quit do this after 2.1"
"So from now, new players will be able to run through while they are still deep inside the story without having to do all those fetch quests that seem unnecessary"
"If you have accepted a quest that got changed or deleted, it will show what to do instead, so those got updated as well"
"EXP and rewards for MSQ was increased, you will reach or even go further than 50 just by doing the MSQ"
"You do not have to do any side quests"
"We plan to do this as well for HW, SB and ShB, so that you can use side quests for your alt jobs"
"As we discussed earlier, you will have to obtain your chocobo and complete the Crystal Tower quest line"
"Unlocking won't be enough, you have to complete it"
"starting in 5.3, you will be able to fly in ARR areas"
"We thought the costs for these updates would be sky high, but the dev team said "We won't be able to ever change it if you argue like that" so we are doing it now"
"You do NOT have to gather aether currents, complete the msq "The Ultima Weapon" and you will unlock flying"
"Your chocobo will be able to fly once you complete the MSQ quest, so the "I believe I can fly" quest that originally made your chocobo fly is getting deleted"
"We didn't add any underwater areas in the ARR areas though"
"People were rumoring on the internet if we were planning to add flying to old areas because of changed collisions and they were right"
"Something additional from Soken: They have to change all of the environment sounds, how they were implemented because the sound was made under the assumption that you can't fly there, so if something sounds wrong, please forgive us, we are going to fix them later on"
"If some environment sounds are wrong, please let us know"