Glenn,
The welding of the tubes into the monoblock would be in lieu of solder, not in combination with solder. Solder would contaminate the weld.

The weld width of an EB or laser weld is very narrow and once normalized and blended, neither the owner nor maybe even an engraver would be the wiser unless bright blueing is done. TC Contenders have either an EB or laser weld holding the lump on the barrels. Likely, the larger framed gun they make also used this process.

The advantage of the monoblock system is that the monoblock could/should be made by the reciever makers and control of the barrel fit is more easily assured.