Is it annoying to upgrade barracks?

Yep, tough process I recently endured again on my TH9 mini. For DE barracks anyway as I like using BAM. so that slowed raid time down a bit.

Boosting is a more affordable way to keep raiding quickly rather than putting gems into a barracks to finish straight away.

Yeah, very annoying. Takes lot of time to completely train your troops especially if you're on trophy hunting mode. Good thing I'm done with those barracks, already maxed out.

It's part and parcel of growing up (upgrading). It builds character (Calvin & Hobbes).

This brings me to unsolicited advise: max all your barracks at your TH level (7, 8, 9) each before upgrade TH. You have to do it sooner or later.