I'm not sure WordPress has downfalls, per se, but it does have purpose; that's an important distinction. If there's a downfall, it's the developers who believe WordPress can do anything "because it's just PHP." I can also dig a hole as deep as you need with a shovel, because it's just dirt. There's a big distance between theoretically possible and feasible.

I hear a lot of people say you should steer away from WP for e-commerce website.

Woo Commerce is fine. You shouldn't "stay away from it" any more than any other tool, you should just know its purpose. I wouldn't pitch Woo Commerce to a giant warehouse looking to go online, I would use Magento. By the same token, Magento is overkill for an indedpendent crafts artist looking to take control of their etsy sales.

The acid test is to simply ask yourself: What sites wouldn't you build with WordPress? If you can't think of an answer, it's probably wise to venture outside WordPress for awhile to see what you find.

With that in mind, there are other things to know when working with WordPress. Not cons, necessarily, just things to keep in mind.

It's largely procedurally coded. Procedural code works, up to a point, but WordPress is beyond that point. It should be OOP, but it never will be. At least not in this version...

The WordPress organization is bent on backward compatibility. This is a blessing and a curse. In the short term, it increases stability. In the long term, it means the same coding standards that WordPress lanuched with are still in place, and a lot has happened since WordPress has launched and a lot is going to happen. The code standards are already starting to show their age beyond the OOP factor. Notably, MVCs such as Symfony and Laravel have become powerful production tools which are modernizing frameworks and making the WordPress codebase look antiquated.

PHP 7 will be out this year. Every benchmark says it will be significantly fast, and you want that extra performance. It is also going to break WordPress, as many deprecated functions are simply being removed. If WordPress maintains their "always backwards compatible" mantra, it will trap WP users on the dull side of the bleeding edge.

It has matured well beyond it's "just a blog" days. I think it's unfair to insist that is WP's only real use. But those roots do start to show if you start to scrutinize it's ability to scale performance, or fit the needs of, say, medium to large size businesses.

Its plugin community is not as co-operative as other communities. There are only a handful of "universally" compatible plugins, the remainder of solutions tend to be "all-in-one" which don't overlap well with other solutions. This makes it easy to go from have nothing to have everything quickly, but it reduces the granularity of control you have over your site.

Still, it doesn't matter if some schmuck, or even many schmucks -me included- tell you about it. It's being used by millions of people. It's the largest community and larges CMS by a long shot. That by itself warrants your consideration when deciding on which tool to choose; they're doing something right.

In the real world, a client doesn't want someone who can echo the sentiments of others, no matter how compelling the blog post you read. A client wants someone who knows how to use the tools necessary to get the job done. Sometimes, your familiarity with something will make it the better tool, but it helps to keep a large arsenal of resources.