The stock Windows terminal experience is awful. Windows has improved markedly recently with `winget`, so maybe they'll get around to fixing the speed sometime, too.
I've never experienced startup times anything close to a minute. Is your computer very old?
I love Powershell and I wish MSFT would put a concerted effort into optimizing its performance.
Just as easily as Aero switched to Metro, syntax in PowerShell will do what they want, despite impacts to your legacy scripting.
The POSIX shell, on the other hand, is a POSIX standard controlled by the Austin group. The classic adaptation is the Debian Dash shell, which is both tiny and fast, and changes are very, very slow.
Dash can be linked with libedit and used as an interactive shell. Everyone should do so, before learning non-standard extensions in Korn, Bash, Zsh, et al.
Shells are a matter of taste to a great extent. These are different envelopes of features, stability, and portability.
POSIX tools are _not_ discoverable!