So, let’s say I’m playing Sigma from just a bit further back than my DPS.
Let’s say they’re Junk and Ashe. Pretty standard picks. For context, let’s say, I also have a Moira and an Ana, because that’s all my healers are willing to play for whatever reason.
The enemy is running hefty damage, though: they have their own Orisa-Sigma, plus a Soldier, Junk, Zen, and Bapt.
My job is not to prevent all that damage. My barrier would last as little as a second against focus fire. My job is to prevent that damage from killing my allies. That means blocking a stray Helix that I can see going towards a wounded ally in my backline, swapping in when Orisa’s breaks just for time enough for my team to return to natural cover, etc., etc.
The sooner they can break my barrier, the sooner they don’t have to deal with it for a 5 second window or more.
Not just whittle down — break. As long as I have a single HP left without the on-break added cooldown, I can still stop Halts, Accretions, 130 damage projectiles with all of 5 HP of barrier, etc…
If I’m less able to weave that barrier in and out to absorb only what damage I need to absorb, rather than what would ultimately only fill my supports’ ults in exchange for their DPS’s, my barrier is more “punishable”.
I can explain in more detail if you need. I’m just not sure which parts of my prior explanation were insufficient.
In the example before, it’d take a moment of delay before Experimental Barrier actually disappears, meaning that if you make a quick use of it to save someone or absorb/prevent something, there’s that much more time for your enemies to chunk it down and ultimately remove the utility of your shield for a while.
Thus the barrier sees fewer vital uses that effectively cost not but, at most, a bit of SPS in order to prevent a fight from being swung against you — stopping Graviton Surge, stopping Biotic Grenade, stopping Halt, stopping Hook, etc. Instead, if the Sigma uses his barrier for something like that, he has to take on some risk of it being chunked down, preventing or discouraging its further use on such for a while.