Is it harder to have a successful Blogspot blog because they lack meta-tags?

I doubt it. I firmly believe the two key ingredients to successful blogging are a lot of stamina (as it takes a lot of time and energy to build a successful blog) and excellent and unique content (because that's what will bring you both readers as well as recommendations/shares). All the other things (platform, meta tags, trackbacks, comments) are just a bonus, but in the big picture pretty much irrelevant. If you don't have the first two none of the others will help you.

The meta-tag issue is really more about content discovery on the platform, than search rankings. If you have a Wordpress (or Tumblr) blog, other people can find your content though the internal search via the meta-tags. It's a social search level on top of the blog CMS. It gives the platform a sense of community, and makes linking to authoritative external content easy. For Blogger/Blogspot, that social search layer is Google Plus. Which also gives you a sense of community, and let's you link to authoritative content easily. Either way, good content will get discovered, it just depends on whether the discovery is driven by an internal or external social layer.

I'm assuming that by "successful," you mean "higher-trafficked?" If so, given a blogspot blog and a wordpress blog with the exact same content and titles and link structure, the wordpress blog would perform better precisely because of the tags. Your content is one way of telling Google to tell searchers that your blog is relevant; your title, permalink, outbound links and tags are other ways. Tags are indexed by Google and other search engines, so a person searching for, say, "southwestern french recipes" has a higher probability of finding your post on foie gras if it's tagged "southwestern french recipes"--even if your content doesn't contain this phrase. That being said, I'm surprised that Blogspot doesn't have tags, as it's part of Google.

Google has never indexed anything based on meta tags, because SEO operators have always tried to game them. So any connection between blogs based on meta tags is purely notional.