Hello I would like to ask if anyone has experience with player characters that have more than 2 classes. (Didn't find an existing thread, apologies if I missed one)

In my current PT I'm at lvl 4 and combined my 2 fav. classes Bard(lvl3)/Ranger(lvl1)
(It's a duergar, wielding 2 hand crossbows. Like it very much so far)
I 'm wondering if I could make a 3 class player : bard/ranger/warlock, but I'm afraid it will lead to catastrophy once I get to face the mighy bosses at the end with max. level of 4 or 5 in each class, and I don't want to waste hundred hours or so to walk into an impossible endgame.

What do you think, is this feasible or better to stick to just 2 classes and raise each to lvl 6 or 7 ?