Does Your Hot Solder Drool and Cover Your Copper Wires Like Hot Butter?

Crimp splices can corrode over time since it is only a surface to surface connection. With solder it is a permanent connection where the metals are actually bonded together. The difference in resistance between copper and solder is negligible for solder joints. I do the same thing you do if I can. The better the connection, the less voltage drop. Voltage drops in connections produce heat which makes them corrode faster.

DC Current flows through the whole wire. What you are talking about is “skin effect” where the current is concentrated on the outer surface of the wire. This happens only at high frequencies.

As evidenced by this thread, there are a lot of different techniques used to solder. If you have a technique that works for you, great! The solder joints don’t care after they are finished. The only exception to this is highly activated fluxes or other corrosive fluxes that can have long term degenerative effects. Those should be thoroughly cleaned off if you use them.