OB1
Jedi Master
What you are suggesting here amounts to, "Since the current CR system is broken, just amp up the CR until the encounter is a proper challenge." That's not the CR system working, it's me fixing the broken CR system.
Or perhaps the problem is that your PCs are over focusing on maximizing combat abilities when they level up.
As with magic items giving real bonus's that make subsequent combats easier, constantly choosing the DPR optimal options for PCs, especially when an entire party of PCs does so, leads to a real and meaningful increase in power of that party against level appropriate challenges.
5e does not require players to maximize the damage output of their characters in order to have a good chance at succeeding at combat encounters. If you prefer to remove as much randomness as possible from those encounters, you can do so, but then why complain afterwards that combat is too easy? It's what you chose!
If that's not what you want, feel free to not always increase your character's primary stat, or take a high DPR feat, and instead choose things that make your character more versatile or interesting to you. As an added bonus, it may also make combat a bit more challenging!