I think from a gameplay approach most builds with dip into three classes (and sometimes into two classes) have disadvantages which might not be compensated by the theoretical benefits they receive. That a build works is not such a proof of anything, because the game is not that difficult.
I experimented a lot with multiclassing, I think I spent the most money on Withers in my current playthough (an exaggeration ...). I currently have a Fighter 4/Warlock 2/Sorcerer 6 build. You have massive disadvantages, one of the biggest of them that you only get 2 feats, a big blow to any build. And you only get lvl 3 spells. But I could tell you why I made the build (although it's quite obvious).
I don't understand the ratio of a Cleric 5/Wizard 1/Bard 6 build. What do you want to achieve? Why is Wizard in the build? Why do you need Bard together with Cleric? In my experience a Cleric is the best with 12 levels. Spirit Guardians are ok but situational. I would hesitate to rely on the spell if I had not advantage in Constitution saving throws. Do you take War Caster as feat, with only two feats available? What are your points in attributes? One of the most important questions, how do you guarantee enough Initiative to always go first, always a bit difficult in a non-Dex build.
