Suffering heart damage after a weapons sale is ambushed by terrorsists, a military industrialist/ playboy builds a hi-tech armoured suit to save his own life and protect his company from the people he trusts.

I would go with something like... "After being captured by terrorists, an egotistical industrialist builds a technological suit of armor to escape and then must confront a twisted version of his own weapon."

How's this?

"After being captured by terrorists, a self-absorbed money-hungry weapons manufacturer constructs a suit of armor to combat evil. But can he save himself and his love interest from the mentor who has stolen his idea for his own corporate greed?"

Hmm, yes I assumed that "playboy" would indicate his selfishness as his character flaw but it could be clearer.

I keep reading conflicting loglines that often suggest being open ended is good but if clarity is key then I should be aiming for shorter, more concise loglines.

It's not more concise :/ but:

"When a flamboyant but self-centred weapons dealer is kidnapped, he must escape by building a powered suit of armour, but when the armour falls into the hands of his corrupt business partner and teacher, he must fight to save the woman he loves and the world itself from the very weapons he created."

Is this clearer?

Thanks for the feedback anyway, I'll keep working on it