Speakin as an engineer I have seen many aircraft with lightning strikes, but the worst damage was a line of 13 burnt rivets across the L1 door. The reason aircraft get grounded is that you must inspect the aircraft which requires a high lift, and usually there is more than one aircraft hit, and only one high lift.
The only emergency I witnessed caused by lightning was a DBA F100 which was hit at rotation. The lightning knocked out BOTH engine oil pressure transmitters. So the crew got two ECAM warnings, each one warning of low oil pressure and recommending engine shut down. Being quick thinking, after shutting down the left engine, they decided to keep the right engine running for a quick circuit!