1. You Need Lots of Plugins For Additional Features
Yessss, but also... not really. If you need an additional feature, you can easily install it directly into your theme. Buuut.... it requires some programming skills.
In any way, if you don't really need something, don't install it and keep your plugin total number at top most 20 so that you don't strangle a website.
2. Frequent Theme and Plugin Updates
You can disable this auto updating in backend and in your server. If you don't know how search online or just ask your service provider. It is really easy to do.
3. Slow Page Speed
You can ping your a page and see what is slowing it down. If you don't need it, remove it, if not - optimize it.
4. Poor SEO Ranking
SEO is crap anyways, and search engines are becoming more and more advanced so machine-made SEO optimized websites are no longer a thing.
5. Website Vulnerability
Choosing a solid service provider and backups.
6. Website Can Go Down Without Notice
Yes, you should monitor your website for downtime.