Wordpress sites slow, looking for different solutions to the problen

I have several sites on Bluehost, all running Wordpress with Divi theme. They are all painfully slow. Bluehost says to go to GTMetrix and fix all the issues. I've tried, using plugins on some sites and using code on others. (EG: used the attached code to defer parsing of javascript on techgardens.com/optical-engineering. GTMetrix still says to defer parsing of javascript. On techgardens.com I have these plugins running: Leverage Browser Caching, Remove Query Strings From Static Resources, WP Super Minify, Far Future Expiration Plugin, but GTMetrix still gives us a bad score and tells me to fix those issues and the site is VERY slow.) The other site on the server is truenasreseller.com.

I have a web developer who says he can fix the issues permanently, but we'd probably need to keep him around. I think this is the way to go, but i'm looking for other solutions to provide as options to the CEO.

Are there web hosts who are wordpress-specific, who provide support on cleaning up wordpress specific problems like the ones listed above?

Any other potential solutions you can see? Thanks, all.
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