Pyro change super welcome~~!
This is a big quality of life improvement, and should help their scaling a bit better without breaking early game. Approval >9000.
Constable being lighter is interesting. It's a slight nerf to BP/cost efficiency, but IMO that's pretty over-rated as a predictor of worker strength.
It builds slower so a mex that would normally be built in 15 seconds will now be built in 18.75. Considering the worker will be there 3 seconds earlier due to 30 less cost, the first mex is coming up .75 seconds later, costing 1.5 metal (assuming mex is worth 2m/s). So you're up 28.5 metal at first mex. However, the second mex will be up 4.5 seconds later, costing 9 metal, bringing you down to 19.5 metal up. Your third mex will be 8.25 seconds late, losing a further 16.5 metal, bringing your saving down to 3. Everything past that goes into loss territory, and it costs extra if you stop to make energy or lotuses.
1 mex - 28.5 metal up
2 mex - 19.5 metal up
3 mex - 3 metal up
So economically it's going to do worse than before if your are immediately slamming four or more mex with it. There will be a short window where you have a small increase in map pressure as a result (+3-30 metal, +1m/s while building) however, and as a support unit it is superior in stats/cost.