Thief rogue in BG3 in general is a little OP with its 2 x bonus attack+hand crossbows. Also a Multiclass isn't gonna destroy anything , like 1 to 6 lvls of lvls of Fighter for action surge and archery fighting style, extra attack and an extra feat / ASI... or 3 to 5 lvls of hunter ranger, for horde breaker, hunter's mark, and extra attack, and archery fighting style. But really if you wanted to 8 lvls fighter+ 4 lvls rogue would give 4 Feats/ ASIs just as some ideas. The most attacks in the game though would be 11 lvls of hunter ranger with the Hunter's volley action wielding 2 hand crossbows / and 1 lvl war cleric. this would give you also divine favor which is better then hunters mark or hex since you don't need to move it and it effects all your attacks, even the ones from part of the volley, also gives horde breaker which works with the hunter's volley action. War cleric also allows you to attack as a bonus action with your weapon if part of an attack action, so would use a longbow or heavy crossbow if crossbow expert is available as a feat in full release before you get volley. Before you get to volley you could still be hitting 3 to 4 targets a round. rogues may have the best single target damage, but hunter rangers excel at damaging multiple targets.
