WordPress Speed Optimisation (Google Insight 80+ Mobile/Desktop)

The website to be worked on is: www.marketinghq.co.uk
It currently uses this theme/demo: https://themes.radiantthemes.com/seolounge/home-version-1/

We have:
Great Host, CDN (WPX) and WP Rocket installed. We've made the site as fast we can with plugins.
This is not the standard install WP Rocket and leave job.

What we need:
Google Page Insights to 80+ for both mobile and desktop.
Whilst keeping the website load time under 1 second (pingdom).
(Possible) A Custom theme which uses only the parts of the site that it currently does.

What we suspect:
We think the theme itself is very clunky (WP Bakery) and is perhaps loading a lot of CSS & JS that it's not using.
For example: https://gtmetrix.com/reports/www.marketinghq.co.uk/j2I9D2h3
If you look at the Waterfall, you can see that it's trying to load an old logo that doesn't exist/ is not used in the design anywhere in additional to number of bloated CSS, JS and fonts that isn't being used.

In summary, the website is finished. All we do now is add portfolio items/ blog posts.
We're looking to have the website looked at by a professional and remove code that is affecting load times in anyway.
Please write 'confirm', to show that you read this. An example of something odd is when loading the page. The main banner image loads small and then fills the banner after a short delay, almost like the page is being made wrong and then corrected.