\documentclass{article}
\usepackage{amsmath}
\def\<#1\>{\begin{align}#1\end{align}}
% ==========
\def\bla#1{
\begin{align}
\textrm{POTATO: }{#1}
\end{align}
}
% ==========
\begin{document}
\<x = 2\>
\bla{x = 2}
Text.
\bla{x = 4}
Text.
\bla{x = 6}
\begin{align}\label{eq:A}
x = 2 \\
x = 4 \\
x = 6
\end{align}
\bla{\label{eq:B} x = 8}
%\bla{\label{eq:C} x = 8 \\ x = 10}
\eqref{eq:A}, \eqref{eq:B}. % \eqref{eq:C}.
\end{document}
When you define a name for your newcommand, it will be recognized at TeXstudio.

autocompletion/autosuggestion works nice.

and, as you said in the question, it works

On the other hand, if you keep environments, you keep some useful tools and flexibility.

It shrinks. (And I personally love it).

It also applies for personal commands with more than one line

But, if you don't think carefully (As I did when trying to recreating the situation) you might have more headaches in the future than you expected.

Oh... and don't get me wrong, I really like to create my own commands

When customizing, you should really try to find a balance (trade-off) between flexibility, readability, usability and organization (and a setup that is a dream for someone might the a nightmare for someone else). The overall suggestion is to look for good practices.
\newcommand. When I define them locally, TeXstudio always recognize them. When I define them in an own package, I need a.cwlfile so that the\newcommands are recognized. I don't use\def, [check this] (https://tex.stackexchange.com/q/655/140133) except when it is the only option. Personally, I would not suggest creating a command to encapsulate an environment. Environments are well recognizable in TeXstudio, simple to identify and the default shortcutCtrl + Eis very useful. – FHZ Mar 31 '20 at 03:30