Not sure what you're trying to say?

Depend's on your team comp. If you have mages on your team that can easily hit multiple targets (Orianna, Katarina and Ziggs are good examples) then Wit's end can work really well. It's particularly effective because your clone applies on-hit effects, so you can administer the -25MR debuff very quickly, rendering affected enemies extremely vulnerable to your teams mages. The perfect scenario is when you play with Orianna. You can send in your clone to start shredding MR (and potentially waste some enemy abilities) before you go in with Ori Ball to decimate the enemy team (or burn some summoners for free). You could even just initiate a fight (with help from a tank) to bait the enemy, then your mages come in to clean up the fight. This works particularly well due to the tankiness in the bruiser build. Another important use of Wit's end is when you're having to duel mages (e.g. when facing Elise who will try and counter jungle). If you need to jump onto an AP champion Wit's end makes it MUCH easier as you gain MR. When the enemy team consists of mostly mages (which is happening more and more *cough* Ziggs Bot Lane *cough*) then the extra MR can be life saving.

However, as you can see it's VERY situational. It's important to consider the item(s) that Wit's end is replacing in the build. Whilst the attack speed and on-hit effects are useful, extra health (or an extra life from GA) can be much more valuable (and normally is). Wit's end basically gives you 65 MR when fully stacked, but Visage & Banshee's give you 55MR and 500 & 300 health respectively, which is obviously much more durability. Furthermore, you might not even get the full Wit's end stacks if you die too fast (due to decreased health) and you lose some synergy with Titanic (but gain a bit due to increased attack speed).

Overall: get Wit's end if you have mages that you know can carry teamfights and if you have at least one tank in your team that can front line. If the mages on your team are struggling or you have no tanks in your team then Wit's end is a waste of money as health (or even flat damage) is more valuable.

So recently i've stopped building protobelt as I normally need to get zhonya or more flat AP to stay relevant at that point in the game. Also, like you mentioned, the shared cooldown can be pretty annoying. I was building both before because they work in different situations: gunblade for single target burst and protobelt to clean up a couple low targets. Another thing i was finding helpful about protobelt was when i'd inevitably sell tiamat, i'd be lacking wave clear. So, i'd protobelt to instantly clear a wave, wait a bit for someone to try and counter push, and try and assassinate them with gunblade.
Overall, go for gunblade! Was my bad for not updating the guide to be fair aha.

Hey :) So the main problem with AS builds are that you die before you're able to output enough dps. With Shaco, an inherently squishy champ with little CC (boxes are all you have), it's better to focus on burst and one-shot potential. When trying to assassinate a carry, if you don't manage to burst them down quick enough you'll just get one-shot yourself (especially if they're not alone). Additionally, you need to consider the build path when going AS. You don't really get the same power spikes you get from items like Gunblade, Lich bane, Tri Force, IE etc. Furthermore, you don't actually get that much AP or AD overall the more hybrid items you get. In fact, you might be seeing diminishing returns in terms of damage compared to more AD/AP focused builds (haven't done the maths though, so don't take my word on it!).
However, AS builds do scale well late game if you build enough health and have decent resistances (scaling Armour & MR runes help a LOT). Also, if you build Wit's end and have at least one strong mage in your team then there's serious teamfight potential. You can jump onto the enemy with your clone and start eroding their MR, which means if your clone explodes it will do plenty of damage alongside the 3 boxes, and your team can clean up easily.
Nevertheless, it could be worth trying out an AS/on-hit build (i'll give it a try!). Maybe Cinderhulk/Bloodrazor, Berserker Greaves/Mobis/Swiftys etc, Titanic, Gunblade, Guinsoos, Nashor's/wit's end.