Learn English – If + past participle

Yes, this is acceptable.

Both your sentences present conditionals; although they are not expressed as formal IF ... THEN constructions, they might easily be so:

The situation would have been worse if he hadn't helped.
It would have caused us a lot of problems if anybody had not cooperated.

The protasis (IF clause) of a conditional may lie outside the sentence at hand; this does not invalidate the use of would:

It looked like the school might have to close. That would have been a shame. = If the school had had to close, it would have been a shame.

All of these uses are equally valid with non-past^✲ reference:

The situation would be worse without his help.
The lack of anybody's cooperation would cause us a lot of problems.
It looks like the school may have to close. That would be a shame.

In fact, most uses of would may be understood as implicitly conditional, though the actual condition implied may be very vague:

I would like a piece of pie. [eg, if you have any or if you would be so kind as to bring me one]
I would be happy to do that for you. [eg, if you were to ask me or if you need help]
I would never say such a thing! [eg, if the opportunity arose or even if I were provoked]

^✲ I should perhaps note that past modal + have + past participle , although it looks like a “perfect” construction, has nothing to do with the ordinary English “perfect”. It is, rather, the language’s workaround for the awkward fact that the modals can, may, shall, will may be used in their “past” forms with non-past (present or future) reference—which leaves them no convenient form for expressing the same modality with past reference. To accomplish that, we employ the “perfect” construction. It would have been is in effect the simple past of It would be.

The sentence is a way of saying:

Angular is what HTML would have been if it had been designed for applications.

In general, phrases of the form "if [noun] [helping verb] [verb]" can be rewritten as "[helping verb] [noun] [verb]".

EDIT: As Colleen pointed out in her comment, helping verbs are also commonly called auxiliary verbs.

Examples:

• If I had been there, I could have stopped it. -> Had I been there, I could have stopped it.
• If John were taller, he could play basketball. -> Were John taller, he could play basketball.
• If the dog would jump, he could escape. -> Would the dog jump, he could escape.