You build according to the gospel of
@Sitting Duck.
He's a man that knows his shit. And he preaches learning to tech for yourself, forget about 90% of the stuff you read both on the internet and in manufacturers descriptions.
Learning to read a manufacturers description for exactly what it is, is a skill. The hype is one of the main selling points to any airsofter, and we get bucket loads of hype with every upgrade.
Basic well picked upgrades can and do make cheap guns brilliant.
Learn to tune a hop and pick a barrel. Those 2 components make 95% of your gains in airsoft on the field. A good barrel and perfect hop will reward you with range and accuracy. The hop unit been plastic metal or other isn't going to affect anything unless the hop is faulty. Spending money on a high end hop unit then trying to tune it is not an easy process. And those people that can build it once and make it look easy - Those guys have built hundreds of hops - it's not the unit that has the magic. And even those guys have troubles when they build on a different model of gun to what they know. Everything is learning.
Learn what basic gearbox upgrades do. And research 13:1 gears and the motors that drive them. A well built 13:1 gearbox with the correct motor will run 7.4v lipo's faster than most stock guns on 11.1v lipo's. And they do it with a fantastic trigger response.
And the biggest tip of all is to learn when not to spend money.
A basic JG or Cyma can outshoot a £400 stock gun. If tuned right and with a little cash spent on the correct upgrades you can make peoples expensive guns look really really bad. Likewise, those modifications done to an absolute stonker of a gun can make it the thing of dreams. So approaching what you see as a problem with an open wallet isn't the best solution most of the time.