Di2, eTap, it's all about personal preference. My year old eTap has been flawless. I charge it about every 30 hours and I do carry a spare battery for insurance in case of battery discharge.
Likewise, my friends with Di2 have been just as happy.
Anyway, never heard of the eTap derailleur failure until BF and I hope the issue gets resolved.
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“Train hard until your legs are tanned, then keep going until the shape arrives.” -Jolanda Neff