We did the Three Lochs Way as part of a day bikecamping from Glasgow to Arrochar last April. Not for the faint of heart if you’re carrying camping gear. There aren’t any bits as bad as the Loch Lomond side carry though.
I think it’s the Killouter Escarpment that was a bit of a challenge fairly near the start. A bit of hike a bike here and there too. Still enjoyed it though. Would recommend it if you’re up for a bit of pushing/carrying. Would likely be much less challenging without a loaded bike.
The next two days were spent going down the Cowal Way to Portavadie. I’ll just describe that as “not for bikecamping”.
There’s a “Three Lochs Way” app that has some good info in it.