I don't have an issue with anyone trying to speed up mobile page loads, anyway you want to do it. I am not personally ever going to strip my forums down to AMP where the site loses all branding and identity, and I am not going to lie awake nights trying to figure out how I can shave another half-second off mobile page loads. At a certain point, you are howling in the wind way past the point of diminishing returns.
With the AMP addon I've been making you are not really giving up much of the "original look/branding" of the site. The non-AMP and AMP pages look very similar, the only major part where it is "noticeable" (if you would open and compare) is the logo position and navbar button. Otherwise everything else is almost identical

For someone landing on your site from a search engine, it doesn't matter. If they start interacting with your site, they will use the real site anyway
And no matter what you do, AdSense and similar advertising networks are still going to be dragging down you page load speeds and there is little or nothing you can do about that except give up the income and stop using ad networks. Not many forum owners are going to do that and smaller and/or newer forums aren't often in a position to be able to sell and host their own ads.
Yes ads are always going to lower the score.
The Pagespeed scores are anyway just an indicator, so try to bring it up as high as possible (without ads) and then add the ads (if you want to monetize).
The added benefit with AMP is that the ads will also be AMP pages, and can't load megabytes of JS that will hog down the main thread.
We keep hearing that faster mobile speeds are coming but they are never going to be able to compete with a fast cable or fiber connection using ethernet.
never say never
I get a 12ms roundtrip latency and 290 mpbs downlink speed straight into my phone, could get 600 or 1000mbps if I paid 5/15€ more per month on my contract
But yeah, mobile connection speed in 99% of the world is quite bad, and in developing countries and the like people won't have high-end phones etc etc.. Maybe the Starlink satellites will help with connection speed soon, one can always hope
Until then we just need to focus on bringing the page load times down instead
Going from 1,500+ KB to under 800+ KB helps. Yes AMP can do the same for you too just you have less control over the process.
On my site with the AMP addon installed and ads enabled, it now loads 728kB of AMP JS, so that is extra JS trimming you could have.
Not to mention that the AMP JS is alo optimized to try and be lightweight, something that can't be guaranteed with non-AMP JS
Disabling ads, the loaded JS size is 543kB, and If I removed the analytics it would be a further 98kB saved
Cheers!