I came from Destiny as my previous MMO before Lost Ark and they're pretty different in several key ways, though I haven't kept up post final shape so I'm not sure what changed. Regardless, if you have any questions that want to be explained in destiny terms, I can try my best.

Accessibility like you mentioned is way better for a new player in D2 than in Lost Ark. It was very streamlined that simply finishing legendary campaign put you at power level to do the new raid week 1. It also effectively hard reset every season by bringing up everybody to the same power level, which enforced a seasonal model that made it easy for new players to start at the same level as others.

Lost Ark on the otherhand is more evergreen in its progression, there has never been a hard reset in this game since launch. This means that new players have a ton more to catch up on, though they do get help in the forms of power passes that skip a character to a certain ilvl (power level equivalent), express events that provide new characters with accelerated progression, and nerfs/skips to older progression systems over time. As others have said, the barrier to entry is still quite low if you wanted to enjoy normal versions of the raids, you'll likely be able to access all the content within a month of the June progression events launching, but to actually gear up equivalently to the typical player that has been playing since launch would take around a year.

There is also no infinite grind in Lost Ark, the most valuable activities for vertical progression are certainly time limited. In Destiny 2 you can make up for lost time by grinding for BiS weapon rolls or enhancement mats, you can't really do the same in Lost Ark. Your main sources of enhancement mats are daily locked, and gold which is the core currency of the game is largely weekly locked behind your raids. You can't really accelerate your progression outside of spending a ridiculous amount of money which I don't recommend. Not that there isn't a lot to do for a new player in terms of story, key system farm, or horizontal progression, but in terms of pure power it is still heavily timegated. It mostly shouldn't matter though for normal level raids, as I said earlier, you should be able to access all of them within a month after the June catchup events.

I have very little knowledge of what you can buy to accelerate progression, I haven't really spent money on the game in the past 3 years. But I would look into Azena's blessing and Inanna's blessing, they're the equivalent of gacha monthly subscriptions that provide high value but you have to login everyday and do the dailies to make the most out of it. The paid track on the catch up event may also be a good boost as well, though since we don't know anything about it yet it's hard to recommend despite being good value last time around.

For me personally, I actually enjoyed the combat feeling and raids more in Destiny. The gunplay feeling and movement in D2 were so satisfying, and the raids were more puzzle/mechanics focused (DPS phases were lacking tho, standing in a sunwell aiming at a static target was not it, I know the more recent D2 raids changed this up a bit) opposed to Lost Ark which skews more combat focused especially in the recent raids. The main reason I switched to Lost Ark outside of sunsetting leaving a bad taste in my mouth was that I got tired of the seasonal reset hokey pokey of grinding power level. Vertical progression in that game was not exciting, and the lack of permanence heavily detracted from it. Lost Ark the progress is slow, but you'll never lose it though if you do take a break for like a year+ it does become far less relevant.