Your Cyborg is Playing Blackjack With a Seven Card Hand
I'm making one major assumption, which is that when you say
"It is about the strength of steel (any shape that steel can hold under any given pressure, this can handle"
that also means it holds rigidity in that shape as if it was made of steel.
In that case, this weapon is absurdly good.
Real melee weapons are all about compromises. A polearm has range and power, but is basically just a stick if someone gets within your guard. A sword gives you speed and versatility, but it's effectively useless against good armor. A mace is a fantastic bludgeoning weapon, but a good shield makes it very hard to get a solid blow in. Few things beat a dagger once you're wrestling on the ground, but it loses to everything else otherwise.
Every weapon has an optimal range, and the half the game of medieval combat was about forcing your opponent to fight at your optimal range while staying out of theirs.
When it comes to that particular game, though, your cyborg is playing blackjack with a seven-card hand while their opponent is drawing off the top of the deck.
Start the fight as a poleaxe. You have reach advantage, which is massive. I'm not saying a poleaxe never loses to a sword, but I'd given about 5:1 odds with armored opponents of similar skill.
So what happens in that 1? That's when the sword-wielder manages to move aggressively enough into your range, likely half-swording, at which point they would have an advantage... against a regular polearm wielder. Instead, you just shrink your weapon to sword length (ideally always just a few inches longer than theirs). At that point, with similar weapons, it should be closer to even odds... except that even at this range, you have a huge advantage. If they try to bind up your weapon, or pin it, you can just shrink it out of the way or change its shape to free it from the bind or unhook it.
Depending on how dynamically/quickly you can change the shape, this gets even more broken. Your blade can grow parrying hooks at will, and vanish them if they're getting in the way. If it can adapt fast enough, the truly OP move is to get them into a bind:
(credit Dequitem on youtube)
and then have your moving metal actually wrap around the blade of their sword, then twist it out of their hands. You can create unescapable blade locks!
To really enhance it, I would pair this weapon with a three-or-four-foot long wooden pole, with holes through it every six inches or so. You can then use that to extend your reach, by having it function as a temporary haft, extending your range by a few feet, with metal bands along the wooden haft to keep hand-contact, (with metal 'dowels' growing through the holes to keep it locked in place) without violating that eight-foot range requirement, and then simply dropping it once they get within that range by having the dowels 'shrink out'.
credit me in fusion360