Both of those reads are wrong.
There are many people into hifi as a hobby who are not after absolute accuracy, and there are also many established, widely respected hifi brands who don’t pursue absolute accuracy in their speaker designs. And I would say the increasingly dominant approach in this hobby, even for the people who are more analytically minded, is to pursue a response that takes cues from one of several psychoacoustic response curves… which are not flat.
And I don’t think there are any experienced mix engineers who just want louder and louder sound. Maybe that’s true of teenagers who are spending money from their summer job on some KRK Rokits at Guitar Center… but music mixing is an actual job, and good mix engineers want one thing from their monitoring, which is mix translation. You want your monitoring to be accurate, with minimal coloration of its own, so that when you play your track back on a different system, you don’t end up with completely unpredictable results. If your system has major nonlinearities and idiosyncrasies that you have to compensate for to get things to sound right, those compensations (which apply to your system and yours only) will end up baked into your mix, and your mixes will translate poorly to any other setup. That means your records will sound bad, and you won’t get hired again.
The SL-1710 is as good or better than the Rega P3 assuming its bearings are good.
If you’re in the US I would not consider Rega. Their price disadvantage here is very steep (the closest matches on features and quality from other brands usually cost about 60% as much) and they lack key features for flexibility and upgradability that you should not be going without in the $1000+ bracket, like adjustable VTA and adjustable azimuth. And the VTA issue in particular will mess you up if you have any intent to use any cartridge not made by Rega (such as a Denon), because their tonearms are set up for their house cartridge height of 14mm, and pretty much all other companies’ carts are 17-18mm or so. (I believe this is true of the Rega OEM arm on the Avid as well, though I can’t find the full specs of that Avid cart.) You’d need to add a spacer to get things aligned.
If you’re in the UK… all this stuff is still true except the pricing part of it. Regas in the UK compete with other brands’ models at more like 80% of the price, not 60%.