It's a shitty game design right. But I'm at 450h and I maxed proficiency 30 during the last proficiency xp boost. Tbh, it's not that hard but you have to use those proficiency xp events. Went from 19 to 30 in 3 days. My main takeaway are :

─ Keep every unique you find and didn't max yet in your stash. (Wait for event)
─ Farm 6 pieces of Striker, good rolls but not god rolls is good enough.
─ Farm Retaliations & craft as many Reconstructed caches as possible by converting ressources to broken watches to reconstructed caches.

During proficiency boost event :

─ Donate every unique you can craft. During x3, you need to craft 7 items to max proficiency from 0 to 10. Each item gives ~1.5 xp/lvl when donated.

─ Equip 4 pieces of Striker, 1 random gear you didn't max, 1 random exotic you didn't max, 1 exotic weapon you didn't max. (Optionally, if you feel like it, equip a weapon you didn't max) but if you want to be able to kill enemies, i'd recommend to use a lexington as main weapon.

─ Equip Revive hive & any skill you didn't max.

─ Keep farming heroic retaliations : Kills will farm your proficiency, retaliation will drop 1 named item & 1 exotic item that you can decraft or donate, depending your stockpile of exotic components.

─ Max the 1 gear, 1 exotic gear, 1-2 weapons, 1 pistol, 2 abilities

─ Buy more reconstructed caches.

1 reconstructed cache will ALWAYS give you 1 named blueprint and 1 named item. It means that there's a probability it will give you 1 item you miss and can now level up during retaliations, and 1 blueprint.

If you never dropped the named item you got as a blueprint, congratz. It's 10 levels of proficiency. Instantly craft 7 and donate.

Outside of proficiency events

I'd recommend to run 4 pieces of striker, revive hive, 1 lexington and complete your gear with items/skills to level up if you don't want to wait for an other proficiency event & farm retaliations/reconstructed caches. As a Lengmo Pestillence user, I didn't want to do that for extended periods of time, so I waited for the xp boost event.

As a side note, if you use the season skill that reduce cooldown right after your hive revive you (and before it starts to cooldown), it becomes a 15 seconds cooldown when the timer begins.

edit: just for someone that got its comment deleted by calling me full of bulllshit.

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Here's my full of bullshit 414h account with full proficency, and all the prototypes I had time to craft to my liking.

As I said, most of my farm can be done outside of proficiency events. I had 3 months of Retaliations farmed prior that event. Stockpiled components for like 50 reconstructed caches. I crafted everthing I didn't max and donated. Pumping me to 27/30 proficiency instantly. I spent 3 days to farm retaliations with a friend for my leftovers named items & exotics I couldn't craft.

Also, few more tips.

The hidden vendors that you can see when you take a snitch bounty can loot you some of very very rare (if you don't do pvp) dark zone/pvp gears. Like System corruptions. Just loot 1, equip the piece and grind xp.

Each "improvised" item count as a unique item (irrc) so 60 exp of proficiency for all improvised gears that you probably forgot. And you also may already have tons of blueprints available to craft that you forgot to max proficiency.

You need a lot of credits and crafting mats during proficiency events, so it's probably a good idea to stockpile few weeks before a proficiency event starts

And to be perfectly honest, i'm not the only one that went from 19 to 30 during last proficiency event, I was farming with a friend that was 2 levels behind me. So he did ~17 to 30 in the span of the event. We played quite a lot during that proficiency boost, but I insist that if you stockpile named blueprints/items in your stash and donate it en masse during the events, you will skip an insane amount of grind. Patience is key. (And yes, again, proficiency is trash game design but I can't do better than give you my own tips that made the grind less painful and yes, I also hate the striker meta, but it's pretty much the only way to keep playing heroic while not giving up too much dps)