Do I really need a plugin manager like vundle?
No. Plugin managers have always been and will always be optional.
What is the utility of such tools, how would it affect my vim ecosystem?
You don't have a "vim ecosystem"; you have a Vim setup.
A plugin manager may be useful if:
- you use too many plugins,
- you like to try new plugins,
- you absolutely want your plugins to be always up-to-date.
If you use too many plugins, the usual installation scheme will likely become too messy very quickly. This will make the process of updating/removing plugins quite a chore. Plugin managers usually keep track of what is installed and where, in order to make the whole thing easier for the user.
If you like to try new plugins, plugin managers usually make it easier to install/remove individual plugins.
If you absolutely want your plugins to be always up-to-date, plugin managers usually give you commands for updating or even auto-updating individual plugins. This more or less guarantees an always up-to-date setup.
If none of the use cases above fits yours then you don't need a plugin manager. But having one won't really hurt anything unless you fail to read and understand its documentation.
Since I don't use many plugins, don't like to try new plugins, and my few plugins are either written by me of very stable/dead, I have zero need for a plugin manager. But I like when my stuff is neat and tidy so I use a runtimepath manager, Pathogen, that lets me keep my plugins in separate directories.