I’ve played a quite a bit of bg3 (and DM’d some DnD) and can offer some thought. Please excuse the wall of text. I wouldn’t go pure rogue, and get eldritch knight, for Weapon Bond. You will lose Reliable Talent, but pushing people isn’t as useful in the third act, where you’d get the feature anyway. Going 3 fighter 9 rogue gets you the weapon bond, weapon and armour proficiencies, and the 5d6 sneak attack bonus on finesse weapons. Your weapon progression won’t be limited to Returning Pike > Nyrulnea & Dwarven thrower plus the stuff you pick up from the ground and instead you’ll get a progression that looks more like Ritual Dagger > Phalar Aluve > Dancing Breeze. All finesse weapons you will be able to bond with. Take thief and you’ll pop out of the shadows with a throw, dash to reposition, and hide again. Great single target damage, and you’ll have plenty of skills to boot.

On the other hand, you could go EK 7 / Thief 3 / Abjuration 3. EK gets spells from the abjuration school natively, weapon bond, and an attack as a bonus action (I think the Throw action counts, but could be wrong), thief gets the extra bonus action, and abjuration wizard lets you learn new spells (up to level 2 spells) and a shield that increases each time you cast an abjuration spell. You’ll get the option to either throw the same weapons mentioned above, protect/heal someone or yourself, or do magic damage. Probably will be harder to manage, and each long rest you’ll want to keep an eye on trader inventories to see if there are any Abjuration spells on sale, but could be more interesting/less monotonous. Stat spread will also be a bit MAD, being Strength, followed by Intelligence and then Constitution. You can get the headband of intellect, however, which will give you a +3 to any Spell Save DC or modifiers.

As for assassin, it works great on characters that can nova. For example, an Oath of Vengeance Paladin with Assassin 3 can blow up single enemies really, really easily (plus, fits thematically, like an inquisitor or something). Give them a finesse weapon (for example, the Shadow Blade), stack some extra damage (with the ring that gives extra psychic damage while concentrating, which the Shadow Blade does), two level 2 Divine Smites, and one off-hand crossbow with the Ne’er Misser, guarantees you will be able to one-turn beefy enemies (especially with the Shadow Blade combo, psychic resistance isn’t common). On a throw build, I can see the appeal, but you’d need to have your rogue start fights, which means they’d be up-front, without much in the way of AC or HP. Thief allows you to stand back a bit. Assassin also falls short later in the game, as some enemies have the Alert feat, which means they cannot be surprised. That, coupled with the low dexterity, means they’d probably go ahead of your character in initiative. Plus, returning weapons (as in, weapons that have the Returning trait) are somewhat bugged. If you start a fight by surprising someone, weapons don’t always return. You could end up wasting the second turn by picking up that weapon and equipping it. I haven’t gotten my EK far enough to test whether Weapon Bond weapons also behave like this, however.