You need to able to set aside your personal issues with me on these forums, I'm not having this nonsense here either. I wasn't even being patronizing in the first place. More or less just stating the fact that you judge the performance of the unit based on their coherent unit performance more or less depending on the army-compositions and general-builds in conjunction with each other. Not "Why is A better then Y - They're technically the same in terms of design" - because at the end of the day, the performance of said unit/ability/etc is based on it's blend-in within it's own army, not compared to another. 
Gaurdians(more dps than tacs with BE)
Yes, like you've stated. It's an upgrade-requirement ontop of it to make it excel. 270 + 70/15. But Regular-Tacs off the gate has higher, better sustain and less prone to suffer damage penalties (3 model vs 5) - Less Guardians , less overall damage-combination. Whereas the Tacticals are more probable to be around for a longer period of time. Needless to say, even Tacs with Sergeant/Sternguards/Weapon Upgrades far excels in the combination of the Full-Auto, but let's ignore that for the sake of ignoring things. 
Apply the rest of the yibberyadda philosophy to the rest of the comparions you made in a nutshell. It's just plain bias perspective on the matter, and it's not exactly subtle. 
Big shootas or Stormboys + Kustom Shoota
Again, DPS-drop-off is higher, and ... we need to kinda of get to the case-of-obvious. Kustom Shoota and Filament are both FAR MORE niché then generalist-preferancial purchase that is the Apo Wargear(Bolter). The Kustom Shoota has far worse scaling performance then the Bolter in terms of yielding a compensation-reward effiency through-out T2/T3 (Hench why Klaw/Bang Bang is purchased more regulary) and same is applied to the Warp Spider Wargear purchase.
The TL;DR version;- Bolter has better general-scaling potency then the other-compared weapon wargear. It also fits the "general" theme of Space Marines being more of a mid-late game race. (Preferably late-game)
- The Other-Comparison Weapons has a higher-reap & reward performance in the early-game. But it's more of a risk-taker and can backfire if it has yielded no substantial agression through-commander damage in the early-stages of the game. They will fall off mid-late game far more then the Bolter, due to generalist-T2 purchases are far more generalistic and idealistic to compliment with their T2 roster. (Albeit, this is far more dependant on the actual players playstyle and how they plan on adapting, but in a general-concensus more or less, this is true) 
In most cases, when you see a Commander having equipped a non- AV weapon, and the rest of this army-composition has no real AV-unit. (Ork, no loota for an example) - You'd be foolished not to capitalize on a forced-purchased purchase, like a Razorback or a Dreadnought, most players of higher calibre would do this.  
 
 Because in an essence, the options becomes linear, and more predictable.
- Purchase YET-another wargear? (Not very likely) - Too much economy sink
- Purchase a Hard-AV weapon(Tankbustas?) - More likely. 
Which leads to the following scenario- Prolonged mid-game skirmishes. >> In favor of Space Marines idealistic design and approach to the game. Orks tech to T3 slowed down.
However, this doesn't mean that going with a straight-victory of purchases. You're obviously going to have to capitalize on your purchases by being agressive and getting damage-done, since you've spent some resources to maintain the foothold of the game in your place. You are more or less, doing what you should be doing. Forcing the player into playing into your hand. He has to adapt to you, not you adapting to him. 
Important!DPS-Drop off from each entity is important to consider under certain circumstances. Space Marines // GK's suffer heavily per each entity, whereas the quantity-model races suffer less, but are more prone to attrition, whereas the quality over quantity are more general-sustainability superiority that outshadows the attrition-based models. So it's easier to mitigate damage from the quantity-models then it is against low-quantity. 
I think I got most said regarding this, and a little-bit more then I would have initially hoped to, but at least it's out there on the table now. Obviously it could be even more elaborate, but in general it's the whole-aspect of the dilemma(lolz)
I hope not this is discussed furthermore, I just hope to see some understanding and I'd encourage people to sit down, take a moment to think of the changes (In general) and see the angle, as to - why it was changed, and why this approach. And dwell into alot of different factors and grow as a player in terms of understanding the game mechanics & design more or less. I love having those really in-depth analysis and conversations with players, I do that on a day-to-day basis more or less these days. 
On another sidenote, I do really despise the simplistic and unelaborate responses or suggestions/feedback that I get also. I mean, they give nothing to go on, nothing that it's based on, more or less just from their perspective on something that was a first-impression or whatever. It's just pointless text that is sent to me, that I'm just baffled about as to "Wat do?" type of situation. Really, really do not like those. NOT. ONE. BIT.  
 
 Speaking of which, I'll never forget that guy who made the most absurd suggestion of all. He actually wanted Fire Dragons to ... have melta bombs, and ACTUALLY wanted individual-unit Stormtroopers to DEAL close-to no damage at all (50 shots to kill 1 Firedragon model) and.... just so much more ridicilous propositions. He kindly reminded me the other day about it infact, and I had the ... well *luxury* of playing with him, and it's no wonder he can't get Fire Dragons to work when he blob-retreats and spams X and A-Move. It's like as if he's just EXPECTING it to work like that.  
 
 Oh well, that's enough for me on that little debate & rant. Oh and, well- I might as well throw this out there instead of PM'ing you Lulgrim, there's this guy who's continously nagging on me for not having "fixed" Artillery-Spotters (Who appearantly have the wrong animation(?)), they should appearantly use the same animations as Kasrkins, or something. I'm not entirely sure, but it's a big deal for him for some strange reason and he doesn't want to play IG because of it. (The guy has a thing for details) 
