Q: Who is stronger, Gilgamesh or Arcueid (30%)? While Arcueid has the strength of 4 Servants, I remember there being a scene in hollow implying that Gil was the equivalent of 5 Servants + a.

A. In the definition of Arcueid's strength, there's this thing where "her output changes according to her opponent". As an absolute order taken from her backup, the planet, she is allowed only an output a little stronger than her opponent. And. Single entity abilities of Arc and Servants are roughly on the same level

Servants use their respective Noble Phantasms while Arc uses her unlimited backup to fight, and differences occur depending on affinity. A simple-is-best Arc is an all rounder, and so generally her chances of winning are only high, but there are those opponents that she just has helplessly awful compatibility with.

For example, in cases where even if the guy's stats are about the same as Arc, he has a ridiculously large number of weapons with high versatility. As the amount Arc is allowed to take out is based on "single entity ability", against types like Gil-sama, well, you see?

And the "5 Servants + a" line is a comparison of simple "firepower". Like with the "corpses", foot soldier level opponents aren't going to be avoiding their attacks, so the ones who'd have the advantage are the ones who have more weapons. The reason why Servants excellent at one-on-one combat didn't stand out in Broad Bridge was because of this. Also, for normal Arc, she would get approximately the equivalent of 2 Servants single entity stats.

“...I see you have light fingers. In that case... how about this?”
With a malicious grin, Gilgamesh deployed his Gate of Babylon over a wide area of the rise.
The entrances to his treasury, deployed so as to surround the archer on all sides, began to twist like a tornado. Then they fired innumerable Noble Phantasms with the force of machine guns, raising a veritable whirlwind of lights and impacts high above the eminence.
Tens, hundreds, thousands of Noble Phantasms poured down on the man who stood in the tornado’s center. They were blades or wisdom; suffering or salvation. There were dragon-slaying long swords; cursed swords that bring ruin; hero-killing spears; formless thunderbolts. The originals of every Noble Phantasm that human hands had ever possessed or created were being hurled out unsparingly. A hellish rain of mankind’s legends, fired from fired from every conceivable angle.
Tine, witnessing that fearsome scene, imagined that not even a single scrap of the archer’s flesh would survive it. As the whirlwind settled, however, it disclosed a sight that betrayed both Gilgamesh and Tine’s expectations — the archer, unharmed and brushing dust from the long cloth that covered his body, and mountains of innumerably Noble Phantasms piled about him.
“Impossible...”
Gilgamesh, in contrast to the wide-eyed Tine, stared wordlessly at his opponent. For a brief while, silence reigned on the rise. Until it was broken by the archer’s stifled laughter.
“He... hehe... he... heh... ha... ha ha...”
There was obvious derision in the sounds audible from beneath the cloth.
“...What’s so funny?” Gilgamesh asked, expressionless.
The archer responded with a single, clearly-spoken word:
“Weak.”
If anyone who had confronted Gilgamesh in the past had heard that word, they would have doubted them man’s sanity.
“...”
It seemed to Tine that the temperature of the area had suddenly and precipitously dropped.
“Blindly hurling your arms... You would do better to throw sand,” the mysterious archer
continued in spite of the atmosphere. “Only a real weakling — or a mindless beast — would be felled by such child’s play.”