Time is money and on the web every millisecond of load time count.
Javascript libraries have become too heavy and css frameworks do not use the most advance capabilities of modern css.
Time to refresh your code and crack down on resource call, scripting and rendering.
One of the main reason I used bootsrap was the grid system, simple and efficient. Nowadays css includes grid-column markup:
https://developer.mozilla.org/en-US/docs/Web/CSS/grid-column
https://drafts.csswg.org/css-grid/#propdef-grid-column
The other good reason I had to use Bootstrap framework was the modals. I like their modals, so much I built a webshop with products popping up in modals. The good thing is that you don’t have to go back and forth product pages and category pages and the down side is that category pages code started to grow a tad whith the store products line up.
Avoid webfonts
Replace glyphicon and fontawesome with css sprites use Hover css selector to change color, icon or size on hover and point to another version of the icon etc.
Inline your scripts
Load essential css and js inline for faster rendering
Avoid libraries. Inline your scripts. Defer everything that can be defered.
Optimize image serving
Use fixed size images and use srcset to load properly sized mobile version.
Lazyload images.
One point I need to clarify is the following: properly displaying compressed images on high DPI screen requires to serve an image larger than the size it will be displayed to accomodate the higher density of screen pixel. The questions being: does it impact user experience positively? and Does it impact SEO positively? And John Müller would proabably answers that only the former matters and he would be right in that respect.