Coming from someone whose PHP skills aren't too shabby but his graphical design skills stink, I'd say no.
From the very beginning of my current project, I've had difficulty finding a partner with strong UI skills. In fact, I chose my early frameworks almost solely upon needing to rely on the UI design of others. UI just isn't a strength. Hell, I don't even match clothes well and (I kid you not) I still keep a note in my phone about which colors of shirts and pants match together.
Although Bootstrap is fat, as you suggest, for someone like me having to do almost all UI on my own and who's been told his logo looks like it was done by a toddler with a large paintbrush, it is wonderful to be able to drop Bootstrap in so I can focus my attention elsewhere. A tool like Pingendo makes it even easier for me.