Wow, opinions vary on this subject. Let me begin by saying that I have been struck by lightning while underway and although electric/electronics were toasted crispy, hull integrity was fine.
Chainplates should be grounded although in point of fact an aluminum mast is the preferred down conductor, being a much better conductor than stainless steel stays. This is the path lightning will try and take and this is where boat lightning protection should be.
Recent information from the lightning capital of the USA. University of Florida
"......If the mast base is on top of the cabin, a downconductor is needed to connect the mast base to the ground strips. Use at least #4 gauge copper with preferably bimetallic copper/stainless connections to prevent galvanic corrosion.
Alternatively, make a strong mechanical connection and additionally braze or solder, to improve the electrical contact and lessen the chance of contact corrosion, then paint with an insulating coating. A keel-stepped mast similarly needs to be connected to the keelbolts with at least #4 gauge copper...."