Seems like (as If)?

Hello, everyone!

1. He seems to be happy.
2. It seems that he is happy. (formal style)
3. It seems like (as if) he is happy. (informal style)

1. Sentence 1 ; I think that 'to infinitive' functions as subject complement (that is, subject + intransitive verb + subject complement).

2. Sentence 2 and 3 ; I think that
1) 'it' functions as extraposed it to put 'end focus',
2) the conjunctions - 'that' and 'like', 'as if' in informal style - lead not a subject complement but a real subject clause (that is, subject + complete intransitive verb + real subject clause).

In above Sentence 2 and 3 'seems' is justified to function as an complete intransitive verb, which leads a real subject clause?

To summarize my questions;

1. the 'seems' in the sentence #1 and #2, 3 are functioning different;
- sentence #1; 'seems' is an incomplete intransitive verb, which leads to infinitive - 'to be' - as a subject complement.
- sentence #2, 3; 'seems' is a complete intransitive verb, which leads with conjunctions - 'that, like, as if' - a real subject clause (not a subject complement clause) due to extraposed it.

2. Thus, the syntax isn't the same between the sentence #1, which begins with the personal pronoun - 'he', and the sentence #2, 3, which begins with the impersonal pronoun - 'it'.

Thanks in advance,