The need for speed: Upgrade EE 2.9 or use Craft?

I currently run my site on EE 2.9.2 with a few 3rd-party plugins [1] and modules [2], and a few custom ones I’ve written.

The template code is fairly dated by now, and I abandoned an update to EE 3 because plugin authors were caught out cold in EE 3’s release timing.

My site receives on average more than 300,000 page views per month but is quite slow, especially on pages with complex templates.

My main objective for an updated site is to improve site speed. My current TTFB is around 1.5s, but can be as high as 10s. The site is also monetised, meaning I run Google AdSense and DFP, have Facebook and email broadcast supplier links, which all cause additional request I have no control over.

I like to have some feedback on the two options that I could take:

a) Upgrade to EE 3, then EE 4 and rewrite my templates.

b) Ditch EE and use Craft instead. (I haven’t used it before.)

Have you had to make a similar decision? What did you choose and why? Or why would you recommend a or b?

Thank you for sharing your insights!

[1] CE Image 1.5.6, Easy JAIL 1.0, Minimee 2.1.13, resource_router 1.1.1, Splitter 2.1, Streeng 1.10.0

[2] CE Cache 1.10.1, Stash 2.6.6