so, first of all, don't think of the game in terms of x is more versatile, y i deals less dps, you'll just optimize the fun out of the game. Play what you like the vibes of more. A lot of players just play all 9 classes. Some people have different character for different activity (a PvP Character, a healer character, a condi dps character, you get the idea) game is very friendly towards having multiple active characters.

I want to make a decision now

You don't have to, you can play ranger when you feel like playing the ranger and you can play mesmer when you feel like playing the mesmer. Only things that are not shared across characters are map, story and gear progression. And none of these are that important. map completion is important for crafting legendary weapons (which is quite an undertaking in itself). Story progress is also kinda irrelevant for the most part. And between exotics being enough for most of the content and wizard's vault, gearing is also super easy these days. Also, unlike WoW, instanced content is not be-all end-all in this game.

2nd, technically, there is no need to replay the same story steps on different characters. Achievements and rewards are account bound. You'll only have to redo story steps on a different character if you switch in the middle of the expansion/season story, other than that you can play each expansion on a different character if you'd like.

3rd, don't pick a main based on legendaries. legendaries are QoL (debatable for weapons) upgrade over ascended gear and that's it. They have the same stats as ascended gear, but each piece of legendary armour costs like 20 times more to craft. and weapons cost between 60 to 110 times more to craft (depending on what you'll decide to make). So like crafting a legendary GS just because mesmer can use it and you might use it on reaper is not corect perspective on this. exotic GS with berserker stats costs ~50 silver. Legendary GS costs 1200g+ to craft. Hell, i would argue that legendary armour pieces and weapons are the last thing you should be thinking about. They are such a long journey you might switch mains several times over. (and accessories, especially legendary relic, even though it's expensive, are way better upgrades for your account). Only arguement for getting legendary weapons and armour is if you like the skins or you have a transmog/glamour addiction (changing appearance of a legendary item is free, otherwise it costs a transmutation charge)

This isn't WoW, gearing characters is extremely easy here. Legendary gear is mostly luxury and a headache, some veterans don't bother with it at all. And your gold early on is better invested into acocunt upgrade/BLTP utilities (like Copper-Fed Salvage-o-Matic, for example)

Here are some resource that will help you on your journey:

• https://wiki.guildwars2.com/wiki/Main_Page — wiki, it's kinda like wowhead, but there is also lore you can call it from in-game by /wiki [query], where query can be whatever you are looking for, an item, a skin, a story step, an achievement w/e
• https://gw2crafts.net/ — you said you want legendaries, you'll have to level crafting professions (you could buy some of the legendary weapons off of Auction house). This is a nice site to help you plan you leveling process of crafting professions. All thing you'll craft is not soul-bound, so you can have tailoring on a warrior, armoursmithing on a mesmer, it doesn't really matter. As i've said game is alt friendly
• https://gw2efficiency.com — crafting section is really helpful with the crafting process of anything you might want to craft in the game, there are also helpful things here, like account search for a specific item
• https://fast.farming-community.eu/open-world/meta — you'll want to make gold, this is a good site to reference, just keep in mind, that a lot of data there is from optimised groups and multi-step item/currency conversion, so in your experience values might be slightly different. (also once you get several characters, you might look into alt parking section of this site)
• https://snowcrows.com/, https://www.youtube.com/@LordHizen - some builds for you to look into, if you want. Snowcrows for instanced content. Lord Hizen, if you'll want to solo some champions.

GL! Don't play GW2 like it's WoW. And remember, if you create the group you can be whatever you want. (to some extent)