其实非常简单，只要把合并单元格挪到下面一格就行了，multirow支持反向合并，而tabularray完全都是另一种思路了，针灸无脑推...

\documentclass[12pt]{ctexart}
\usepackage{lipsum}
\usepackage{amsmath}
\usepackage{multirow}
\usepackage{colortbl}
\usepackage{xcolor}
\usepackage{tabularray}
\begin{document}
    \begin{tabular}{|c|*{3}{>{\columncolor[gray]{.9}}c|}}
        \hline
        \rowcolor{cyan}
        $\beta$ & $50$ & $100$ & $150$ \\
        \hiderowcolors
        \hline
        \cellcolor{orange!60}
        & AAA & BBB & CCC \\
        \arrayrulecolor{red}
        \cline{2-4}
        \arrayrulecolor{black}
        \cellcolor{orange!60}% difficulty with multirow...
        \multirow{-2}{*}{静态工作点} & DDD & EEE & FFF \\
        \hline
        \multirow{2}{*}{动态工作点} & AAA & BBB & CCC \\
        \arrayrulecolor{cyan}
        \cline{2-4}
        \arrayrulecolor{black}
        & DDD & EEE & FFF \\
        \hline
        \multirow{2}{*}{等离子态工作点} & AAA & BBB & CCC \\
        \arrayrulecolor{violet}
        \cline{2-4}
        \arrayrulecolor{black}
        & DDD & EEE & FFF \\
        \hline
    \end{tabular}
\end{document}

我是这么理解的：三个 TikZ 环境相当于三个水平盒子，由于长度问题不能放在同一行，所以该自定义命令总体是按照段落模式确定基线的，所以产生了你说的垂直空白。

以下给出一种思路以参考：

以下为代码：

\documentclass[UTF8]{ctexart}
\usepackage{tikz}
    \usetikzlibrary{calc}
\usepackage{geometry}
    \geometry{showframe,margin=.5cm,papersize={16cm,20cm}}
\newcommand\nicetitleA[1]{\vskip1.5ex
    \centerline{\tikz
       {\node (#1) at (.5\textwidth,0) [align=center] {\Huge\bfseries #1};
        \draw [dashed,red,thick]  
            (.1\textwidth,0 |- #1.north west) -- 
            (#1.north east -| .9\textwidth,0);
        \draw [dashed,cyan,thick] 
            (.1\textwidth,0 |- #1.south west) -- 
            (#1.south east -| .9\textwidth,0);
       }%
    }
} 
\newcommand\nicetitleB[1]{\vskip1.5ex
    \centerline{\tikz
       {\node (#1) at (.5\textwidth,0) 
            [text width=.65\textwidth,align=center] {\Huge\bfseries #1};
        \draw [dashed,red,thick]  
            ($(.1\textwidth,0 |- #1.north west)+(0,.5cm)$) -- 
            ($(#1.north east -| .9\textwidth,0)+(0,.5cm)$);
        \draw [dashed,cyan,thick] 
            ($(.1\textwidth,0 |- #1.south west)+(0,-.5cm)$) -- 
            ($(#1.south east -| .9\textwidth,0)+(0,-.5cm)$);
       }%
    }
} 
\newcommand\zhlipsumX{劳仑衣普桑，认至将指点效则机，最你更枝。想极整月正进好志次回总般，段然取向使张规军证回，世市总李率英茄持伴。用阶千样响领交出，器程办管据家元写，名其直金团。化达书据始价算每百青，金低给天济办作照明，取路豆学丽适市确。}
\begin{document}
\zhlipsumX

\nicetitleA{去吧，皮卡丘！}

\zhlipsumX

\nicetitleA{回来吧，皮卡丘！}

\zhlipsumX

\nicetitleB{该你上场了，妙蛙种子！}

\zhlipsumX

\nicetitleB{Come back soon!我亲爱的妙蛙种子！}

\zhlipsumX
\end{document}