Re: I think I hate my Fender.
I have the same problem with my blackface Fenders. I can't even come close to getting to the sweet spot.
Vintage Marshalls will be the same way... they have sweet spots too.
I borrowed a bunch of dirt pedals last Summer and put them all through the ringer. I jived with like one of several that I borrowed.
Then Agileguy_101 turned me on to Weehbo pedals and I picked up a JMP Drive. When I brought it home, it sounded exactly like the demo and all was good.
It turned out to get "my sound" I had to goose the JMP Drive with an old MIJ CS-3 and then another gain stage from my Badgerplex AC after the JMP Drive and before the amp.
But I had it outfitted with the perfect distortion and my clean sound was pure crap at low volumes.
Then I recently swapped the Jensen for a g10 Greenback... and I picked up an Empress ParaEQ to take off of the sub bass, boost the low mids and cut a harsh upper mid resonance.
Now my clean sound is as good as my distorted sound but it was a long haul. I'm a tone dependent guitar player... if I ain't got the tone, I ain't playing.
The Fender Deluxe is a much warmer, less harsh and less spikey version of my Princeton Reverb... I'm surprised you are having so much treble with it.
Of course, I play out of real blackface Fenders, not reissues. I have access to a real blackface Deluxe Reverb and it is tone for dayz.
I would definitely swap the speaker out since if you eventually have to sell it, you can keep the new speaker.
There are sooooo many 12" speakers out there. Being in the UK, I'd just go Blue, Gold or Creamback... the Greenback might break up too early.