Connect to main

We are having an irrigation system installed. The plumber is here connecting to our main line. What he has done is nothing like I have ever seen, though he says it will be fine. We are on a well so my main runs in with a 1" pvc flex to the baffle/pressure tank. comes out with 1" galv. pipe and reduces to a 3/4' valve then feeds the house. He has cut the 3/4' line after the valve and installed a 3/4 x 3/4 x 1" T. The 1" is what he is running to feed the irrigation system. I would have removed the reducer, replaced the 3/4" valve with a 1" then installed a 1"x 3/4"x 1" T and moved on. It just doesn't seem right to feed a 1" pipe with a 3/4 ". Who is right?

A small section of 3/4" isn't going to have much effect.
With city water, the setters are 5/8" or 3/4", and we run 1" or 1-1/4" off of those.
A long distance of 3/4" would have been more of a worry, the distance adding to the friction loss.

If you look at a hosebib, the port that the water comes through is very small. And yet it will gush out of there.