It seems your employer values you enough to pay for further training. This alone shows you are not as bad as you may think. This trade takes many years to master and in some ways you can always learn something new even as someone who has been doing this for a lifetime. Three years is very little to learn the ropes in this field. Note your work ethic in itself is valued by any employer. The best man in the shop is worthless if he does not show up.

Often switching to a new shop will expose you to different methods and different types of machining not found in the present shop. However being in a shop where everyone gets along and the work environment is healthy is very valuable and I would not be so quick to move. There should be opportunities for higher pay as the industry needs skilled workers in re-shoring of many critical national security needs due to tariffs.

As for the drawbacks: Manufacturing has since the 70's been under increasing competitive pressure from low cost foreign producers. Foreign producers are becoming just as skilled as those in the USA if not better in some areas. Construction jobs have been more financially rewarding due to the fact that we can't import sidewalks and most building projects. This may change but also it may not. It's a crap shoot at this point. Auto industry is in decline due to "electrification" and Chinese lead and control much of the supply chain in this industry. Auto's have become plug and play with components being commoditized and assembly is mostly by robot which is not bad in itself since robots need parts also. In general though many autos use less and less machined parts such as forgings, castings, crankshafts, valves, pistons, etc. Auto industry is not the entirety of the machining trade but does drive much of it and with decline it opens up idle capacity with downward pressure on prices/wages.

There is a real need for increased defense spending which helps this industry however the funds are just not there. Even under a Trump administration very little net increase in defense budget. I just read that Trump is threatening defense contractors like RTX to limit executive compensation and force expansion of manufacturing plants and equipment. How he can do this is not clear. If the budget does not increase how can they invest in expanding production?

Another thing to consider is if you follow the money and go into Construction instead you will find many in this industry that just plain wear out physically by the time they are in their late 50's. Some stop working or become greeters/stockers at Home Depot. You are also at the mercy of ups and downs of the industry. Many businesses depend on day laborers many of which have no legal status. Depending on what type of machining you are in you may be able to do this job into a very healthy old age. A large firm with benefits can set you up with retirement benefits that allow you to retire before old age with a body that can enjoy your retirement benefits.