What difficulty are you playing on? I'm always a bit hesitant to applaud those who say that the game is very easy no matter what, also or especially in Honour mode solo runs (I never saw real gameplay in solo runs, just cheese), there are at least some differences which might influence. However, you can actually not hit a brick of wall after x hours of gameplay in this game because you can always respecc and realign. I see that as a great fun aspect, as I'm not a masochistic old school RPG enthusiast, I like experimenting. Try things out.
As much as I like Warlock, I think Sorcerer might be a better dip. Especially if you want to use the Bard for control spells. Control spells in my game have the unpleasant property to not hit when it is necessary the most, despite amassing Spell DC. The Sorcerer by metamagic can give disadvantage to saving throw spells which is a huge help in some situations. I changed my plans for my build in my current Custom mode run at lvl 5 because enemies are so buffed up and I seem to need control spells, I will go Sorcerer for 6 or 8 levels.
BTW heavy armor is not that good in the game. You can achieve the same or better with medium armor as long as you invest in Dexterity (a good attribute because it also raises initiative). Before the last fights in my Honour mode run my Shadowheart with the best heavy armor in the game has AC 26 unbuffed, Astarion with medium armor has AC 25. So I find the dip into Ranger not that convincing, especially as good heavy armor is not present in early levels. It's good however if you want Sleight of Hand from him.
