I never saw the point in being so conscientious about halting the spread of the biomes, except maybe a little area around your home. Otherwise they spread slowly enough that by the time they've taken over most of the world, you've got the gear that they aren't an issue. Maybe people just play a lot more slowly then me, or leave their servers on or something, but I found that in my medium world even by the end of my play though there was still quite a bit of uncorrupted area left.
At least for me, it's not a matter of difficulty. Yeah, you'll absolutely be able to handle the mobs and other dangers by the time it's taken over most of the world, so it's not so much that as it is the
principle of the matter. This is *my* world, I've put a lot of time into it, and I've taken to liking it the way it is... I'd rather not have it just decide to stomp all over everything and convert the entire world into one of two biomes and make it so I can't escape that
damned music. And trying to clean it up
after it's contaminated something? Hah, not likely... The clentaminator is bloody expensive to purchase and use, doesn't have a large enough AoE or reliability to make it worth using outside of controlled projects, and is fighting against a spread that's so fast you can actively see it reclaiming the blocks you've just hosed down.
A large enough contaminated area is pretty much a lost cause; trying to turn it into something that ISN'T corruption or hallow is just going to be an exercise in monotony at best, futility at worst. You're better off just blowing it up as far as time and resource investments are concerned.
I just don't like the game deciding that it's going to steamroll all the varied and interesting environments in the game and turn them into a gigantic monochromatic blob of heightened-spawnrate annoyance, and that I don't really get to have a say in the matter. Even killing off Plantera just
slows the spread, it doesn't stop it or revert it to the manageable pre-hardmode spread that doesn't go through stone blocks. And it even affects the gameplay, technically... You can effectively lose the underground jungle thanks to how corruption/crimson spread works, meaning that all the resources, mobs and fishing tables for the jungle get lost unless you build your own artificial version with blackjack and hookers.
And there are also a number of quest fish that only spawn in underground "forest" areas, meaning an area that is neither hallowed nor corrupted. Those areas can get increasingly difficult to find if you're not staying on top of the problem.
indeed, Jungle Armor is the end of Pre-Hardmode for mage, well, Meteorite Armor is good too but its mostly built around the Space Gun. the Wizard set (and the Gypsy Set) are more for early game. 15% increase magic damage is good but unless you're good at dodging its better to have more defense.
the Diamond Staff is like the Platinum Sword, its the best bang for your buck on the early game but you will have to move onto other magic weapons as you advance. if you reached hell the Demon Scythe should suffice unless you want to go for the Bee Gun or the Dungeon related ones.
i wish they would buff the Amber Staff. maybe even put it above Diamond in terms of quality, yeah a Diamond is the most rare and powerfull gem but for all the annoyance of harvesting the fossils the Amber should be the higher end from all the gem based staves.
Actually, the wizard set with gypsy robes can hit considerably higher crit and damage levels for magic items if you give them meteorite or even jungle pants. Remember that the "set" is just two items, so you can slap on any shoes you feel like wearing, and the overall bonus is actually quite significant. Yes, the jungle set will have slightly more mana (anywhere between 20-60 more mana, all depending) and defense (I believe it's 8 points difference if using jungle boots, don't recall offhand), but the jungle suit DPS can't compete with gypsy+wizard hat. And in Terraria, especially in expert mode, the best defense is a good offense... Dead enemies don't bite.
As for amber vs. diamond, yeaaah... It's kinda hard to say. Yeah, I had a diamond staff before I had an amber staff, but the only thing standing in the way of making amber staves is getting that first extractinator. If you're lucky with chests, you can find an early extractor and start spewing out amber staves like nothing.
The whole gem staff line is honestly a bit of an oddball. Generally speaking, unless you're specifically aware of where you're going and what you're doing, by the time you've scraped together the resources to afford a decent gem staff, you'll already have a couple alternatives that are far more attractive... Hell, I'd probably rather go for meteor suit+gun over a different magic set with a staff just because of the utility the spam gun gives you. A vilethorn with a decent modifier would also be far more up my alley than a frankly rather mana-expensive gem staff.
I'd probably just as soon use the fossils for making a spare fossil armor set or some javelins/throwing daggers. That armor set is actually capable of some pretty beastly pre-hardmode DPS thanks to how it works, and it's all sorts of pound town with the bone glove in expert mode. Just buying a stockpile of grenades and using those can be frighteningly effective, and I'd argue that they're the best candidates for using the hive pack thanks to the huge bonus the set gives to using beenades.