You can look at the issue two ways.

1. The niche companies know where to link etc..
2. Non-niche companies can find these places.
I think because of content creation that it's better to take the niche..

It is hard for me to become die hard on either side. Like everyone else has said having an industry specific target may give you an edge, you maybe missing out on new ideas and info. That is of course in the world of freelance Seo's. Other SEO's focus on what the company they work for focuses on as their target markets.

Many SEO's are probably not focusing on one or two niche's only, but rather on multiple markets at the same time. For me this depends on where these marketers are in the world and what the current trends are in their specific region and also the level of SEO experience that they have. I think you'll find that the more experience an SEO has the more he will move into a certain niche, the less experience SEO's will probably move in multiple niches. would you agree?

I think better to be specialist in all industry from where we are getting business unless we have to struggle for food.

Who would argue that experience is better than lack of experience? Nobody? Then why even wonder if someone with experience in 5 industries is better or not than someone with experience in just 2. It is a side issue. What matters is the amount of RELEVANT experience.

Personally, I always want an SEO who can demonstrate success in multiple sectors. Not one who simply has one powerful site to link from on a particular niche.

Just like a sport player benefits from cross-training, so will any professional benefit from insight and experience they would not get in their normal field.

SEO specialists are often just a little too focused in one direction, which acts like blinkers for seeing wider opportunities, or learning lessons from other fields.

I do encourage people to specialise their skills, for sure, but never, EVER to the exclusion of all else. Check they are a specialist by choice, and not just because they can only succeed at all in one vertical.

Industry experience always have advantage because if one have more experience in a specific industry he will know all the techniques to get better rank

Better question is whether you need to understand the business/industry. In that case it likely is a huge advantage. It's no accident I can do well in RE where I was an agent, property manager and have built houses from literally from the ground up. Someone with actual experience and understanding of the business/industry, no matter the SEO skill level, has a distinct advantage in their familiarity with the lingo, buyer needs and sale triggers. SEO is SEO. There isn't much SEO that is industry specific. Every industry has niches how you find them doesn't change much from industry to industry.