That is an extraordinarily lofty assumption when you're talking about a game that includes a Power-Up Part specifically designed to extend your invulnerability time.
That is not sufficient evidence to claim that D. Barrier, and by extension damage invincibility, was meant to be used to obtain said items, and for two reasons:
1. Many, if not all the areas that you can use invincibility frames to bypass requirements do not require additional invincibility frames, i.e. D. Barrier, to access. I can pass all 3 segments without the aid of D. Barrier.
2. D. Barrier is a defensive upgrade, i.e. you are expected to take less damage because you have longer invincibility. This is the intended
purpose of the upgrade, not
to let you get items that otherwise require other tools (which is very clearly an exploit).
It may be fun to mention that in X5, Skiver's capsule cannot possibly be reached as Zero without such an exploit.
First of all, the Zero Virus invincibility was very obviously not intended (the argument of existing dialogue is negated because Falcon Body and Gaea Head cannot be accessed by Zero without hacking).
Secondly, you can also get Gaea Armor with just Wing Spiral and Firefly Laser alone. So if you're going to include all possible exploits/methods, then by your logic, X5 does not force you to get Falcon before Gaea (this is even excluding the fact you can also replace Wing Spiral with Zero and Crescent Sword/Jumper).
Okay, here's my problem with that statement, which is simultaneously what happens to be one of my biggest gripes with X5: There isn't SUPPOSED to be a sequence to break in the first place. Mega Man games and especially X-series games sell on their non-linear nature, what with the Stage Select screen and all. It's not "exploration" like Metroidvania, but it is meant to be flexible. One or two power-ups to unlock further secrets is done every now and then, yes. However, requiring four or more separate power-ups before obtaining another is something that, outside of X5, was previously reserved ONLY for end-of-game secrets. This is why requiring a COMPLETE armor to obtain part of a second armor is BS design.
When I say sequence breaking, I am referring to any intended sequence where the player is expected to go through A before B, otherwise B cannot happen. The entire Mega Man X series DOES have these sequences, even the very, VERY nonlinear X2 and X4. You can't get Web Spider's or Frost Walrus Heart Tank without Rising Fire/Ryuenjin, you can't get Third Armor's Helmet without first getting Charged Triad Thunder (excluding reverse-engineered passwords), you can't even fight the 8 Mavericks without having first beat the intro stage.
A sequence break is ANYTHING that would disregard what is otherwise an expected A. You are supposed to use Charged Bubble Spray to get Bubble Crab's E-Tank, but physics exploits using slopes allows you to disregard said requirement. In Super Metroid, you are supposed to fight Spore Spawn in order to acquire Super Missiles, but using the Mockball glitch can get you a Super Missile expansion even before you fight the boss (and in combination with very specific screen scrolling or Crystal Flash exploiting, you can even get the Super Missile guarded by Spore Spawn without even fighting him).
A sequence break can be intentional, such as in the case of Super Metroid and Wall Jumping. However, often times sequence breaking is the result of unintended exploiting and glitching. In said cases, while the player is free to abuse them in order to further their enjoyment of a game, unintended sequence breaking is NOT something that you credit the developers/designer for (hence unintended).
While X5 has the issue of way too many forced sequences, the problem with X6 is that X6 is littered
with unintended sequence breaks, where it becomes apparent that X6 would otherwise have almost as much if not just as many forced sequences as X5. Of course, I can't prove to you each and every case of sequence breaking was unintended, but the glaring amounts of inept game design (*cough* Gate's Lab 2 *cough* infinite retries *cough* Sentsuizan button mapping *cough*) and quoted rushed development should suggest to you otherwise. And if they were
intended, why the [tornado fang] were they "meticulously" designing open-ended upgrades when they should have been designing fun, coherent, and consistent stage designs.
So why do I praise Super Metroid for all its exploitable glitches and not X6? Because Super Metroid is actually an extremely good game even without the exploits, and the exploits serve to expand the experience of Super Metroid by reinvigorating its design through intricate yet rewarding shortcuts. On the other hand, X6 is an absurdly broken game where the exploits merely exemplify those characteristics.
To be clear, it's not that I HAVEN'T gotten there with Gaia, it's that the level of memorization and handicap is uncalled for.
Zero Virus Stage 1 is practically entirely trial and error, handicapped or not. That said, I don't find the difficulty for Gaea unjustified, considering how easy the boss is with Gaea.
Also, Zero Virus 1 with Gaea isn't THAT
hard. Not saying I can do it on my first try, but there are much harder things to complain about in the X series, like beating Launch Octopus naked.
The Armor sequence in X5 IS real annoying. That said, back when I was a kid, it's not like I cared or noticed really. I still don't, what bothers me more is [parasitic bomb] like the Gaia helmet being so [tornado fang]ing difficult to get, requiring you to navigate a firefly through that mini maze for a part that does absolutely NOTHING. That's something that you CAN [tornado fang] up, and have to die or retry the stage. if you told me Gaia arms, well, alright. put the helmet in Spike Rosered's stage, the easiest and most obvious Gaia piece to get.
Well, given the fact that X5 has infinite retries (unless you care about Hunter rank), the game actually gives you infinite tries at Gaea Helmet because it spawns you right before the pit and restores your Weapon Energy.