I made another thread on this but it got into the precise technicalities and details of how much mass upgrading mexes unassisted uses compared to assisted so I will start a new one.
Just had a game today where the guy had a bigger eco than me at the end but it didn't seem to affect his map control. When I confronted him on it, he says he "upgraded them one at a time, unassisted". This is the least effective method, however in practice it seems very convenient. Assisting mexes stalls you're eco, upgrading them unassisted is a much smaller drain on eco.
I feel like if I upgraded my mexes unassisted like I used to do then I could have a much better eco, instead of having a team of engineers going around assisting them stalling my economy. I know pros say that assisting is better but it seems strange to me because you really have to watch yourself when assisting the mexes with engineers and you have to plan a lot more due to the economic stall that it causes.