My main character is a Human (Variant) Cleric 1 (Life), Warlock 2 (OOP), Bard X (Lore), which is currently level 9 (so 6th level Bard). It is pretty amazing. He wears a breastplate +1, a shield, and wield the Staff of Defense from Lost Mines of Phandelver, making him AC 20 normally, and 25 with Shield from the staff. I use the staff as a warlock focus and simply holster it as my free item interaction when I want to cast a Bard spell (giving him a free hand to cast).
The warlock levels gives him a powerful Eldritch Blast for at-will damage, 120ft darkvision, telepathy, some spell choices, and 2 1st level spell slots that recharge on a short rest. I often use those spells slots for Bless, Faerie Fire, Hex, Goodberry (via Magical Secrets), Healing Word, or whatever utility spell is needed at the moment.
The cleric level gives me access to armor, Disciple of Life for great healing, and a nice selection of 1st level spells to use with my warlock spell slots. The spell progression also adds directly to bard, though my bard KNOWN spells and progression does suffer some.
The Lore Bard levels gives excellent spell selection (whoever said bard spells are "meh" is nuts), skill access, expertise, cutting words, and magical secrets.
Sure, I don't have access to higher level spells as early as pure casters, but most of them can't go all day long doing a little bit of everything under the sun quite like this character can. And it isn't like I'm doing it poorly either. I easily beat them on survivability, while they beat me on punching with a big spell here and there. I'll take that trade off. I've also noticed that the spells I want to use most often tend to not be higher than 3rd level anyway (like Hypnotic Pattern). I could see using Polymorph more when I get 4th level spells next level, but I don't find myself missing it with the other options I have.