Those synergies extended way beyond the technological too, which is how GE managed to survive in such a dysfunctional state for so long. Once they figured out that GE Capital could capture the financiers' profit margin on top of all their capital equipment, they unlocked a lot of money that had previous been taken up by banks and other investors. I.e. the total interest on a 10 year loan to buy a $10 million engine at 5% is over $2 million - essentially doubling (or better) their profit margins. Between that extra profit and related financial engineering, they could make a lot of money on the backend and turn that into an even bigger financial empire.
It wasn't until the 2008 GFC crushed GE Capital that it all started to really come apart, many decades after Welch got started.