most people don't know what they are talking about when it comes to boats, they rationalize some whacky stuff.
If non-tinned wire was against ABYC codes then all boat makers are going against abyc codes because i have not seen any installed by the boat builder- my 2002 bayliner, and a grady white to be specific. tinned wire is aftermarket, and deceptively marketed.
if you can crimp a wire connector you can solder. there's not much skill needed, or if a person thinks it requires skill then they probably shouldn't be operating a boat to begin with. The ideal way is to do a regular crimp on a tinned connector then hit it with solder over the copper wire. A 60/40 tin/lead solder is highly corrosion resistant and will prevent corrosion from creeping in between the crimp. and a solder connection is far stronger, stronger than the copper wire itself.