If it's done rarely and the content is inconsequential (weapon, costume, useless junk), then it doesn't matter.
But Day One DLC and On-Disk DLC are ways that a company can wrangle more money out of their customers when said customers already paid for the main game. Day 1 DLC is borderline sketchy while on-disk DLC is technically a scam.
Take Street Fighter vs Tekken for instance. Hackers discovered that over 12 characters were disk locked to the console versions and yet Capcom was charging 20 dollars for them as dlc. How is it ethical or good to charge players for something that's already in the game?
Then you've got Javik from ME3 where hackers also discovered that he was already on the disk and yet he was charged as a 10 dollar day one dlc offering when he clearly should've been in the main game itself.
Situations like these render the quality of the dlc pointless if the content is either already on the disk or should clearly be in the main game, but was separated to gouge more money from it's customers. Worst yet, is that several companies have been pulling these stunts and others like them...looking at you Halo 4.
Fortunately, Inquisition apparently hasn't been involved in the above, so there's hope for BW in regards to learning from their past mistakes.
Javik was not on the disk, place holders where on the disk for Javik, to attach the final product to, but he was in no way a complete character. There are a lot of myths when it comes to Day One DLC, myths pushed as a narrative by YouTube personalities who really should know better at this point. I actually think they likely do know better, but actually coming out and saying it, risks angering their vocal viewers and thus hurting their viewership, so they don't.
Ask a Game Dev gives a better explanation of Day One DLC, and the whole development cycle, and how it all plays into it. During Game Dev now and forever, a lot of content is cut, before DLC this content had one of two fates as far as that game went. It either stayed on the cutting room floor or it got picked up and used in expansions, but with DLC a third option was added, it could be used as DLC. Day One DLC has another factor working for it, there is a period between a game going for Cert and game arriving on the shop shelves where, staff where not actually doing anything. During Cert they had to still come into work, to be ready in case the Cert process uncovered some glaring fault, so they could fix it, and resubmit to hopefully still make their release day, but if no problem arose, you had people with no work to do.
Again from ask a Game Dev, he describes in the past epic Nerf Gun wars around a studio in this time, which sounds a lot of fun but, you can understand that the guys paying the bills where maybe not so much a fan of this period. Then along comes DLC, if you give these folks a smaller budget they can pick some stuff off the cutting room floor and work on it, instead of having Nerf Gun Wars, they can be producing content for sale, obviously to the publishers and money men this is a obvious choice. This DLC content is also a lot easier to get through Cert as it is smaller much smaller, and you don't have to produce anything for the stores, you can work on it pretty much up to the day of release. For the most part through if Day One DLC did not exist the stuff released as Day One DLC would not be in the game, it would still be on the cutting room floor never to see the light of day.
As for pricing, others have said it, but prices are fixed by what the market is willing to pay. this is why in Real Terms Games are getting cheaper because people are unwilling to pay more even as inflation rises. DLC is priced at the point the market is willing to pay as well, and will likely stay around those price ranges for sometime to come, meaning that it will get cheaper in real terms, even as the production costs rise. This is fantastic value for money then.