1. Do you find this sentence wrong? Does it sound strange to you?
2. And do you think that a form must be used to be correct?
In my opinion, the sentence proves the usefulness of the passive form "lacked".
Different questions there.;-)
You may have noticed in other threads that I tend to avoid the words 'correct' and 'incorrect', preferreing 'acceptable' and 'unacceptable'
In talking about 'Vitamin A is lacked in one's body', I said, "we don't say that" - a view I still hold.
In talking about 'Vitamin A is lacking in one's body', I said, "You may consider it improper, but the verb is sometimes used in this way." I still think this.
If someone had asked me about 'Manufacturing paint requires high levels of both technical expertise and financial resources
lacked by many would-be competitors', I might well have said, "Unusual, but it sounds OK to me". I simply questioned your bold asserion, with 'is' italicised for (I assume) emphasis, "the sentence below
is correct". I still question it.
Also, I think it's not readily rephrasable [...]. I would have to use a subordinate clause to rephrase it, which would be longer and less convenient. [...] In my opinion, the sentence proves the usefulness of the passive form "lacked".
Manufacturing paint requires high levels of both technical expertise and financial resources, which many would-be competitors lack.
That is hardly longer or less convenient, BC.
I think it's correct to use this word even if it's not in the dictionaries)
I doubt if many people would get upset if you did, but I don't know about Cambridge or TOEFL examiners. I wouldn't advise examination candidates to use it.
And do you think that a form must be used to be correct?
I think that if a form appears to be ill-formed according to what is currently accepted, then more evidence of its use than two citations would be helpful in deciding to recommend it as acceptable. I know that's the answer one would expect of a politician, but I think it's appropriate here. Who are you (who am I?) to say that a form previously unused is 'correct' just because it's 'syntactically fine, logical, convenient and easily understood'?