I don't believe there are a number of "best" brands. In my Highlander voice, "there can be only one." There are many offerrings that are very very good. For me, the evaluation of the best is one that can handle the most extreme condition: water temperatures close to freezing. Handling O2 up to 100% is another (rules out titanium that you said you liked).
There's just way too many outlandish claims being made in this thread and others in which no backing data is ever provided.
What advantages does the glass fiber content give? Just strength? If so, how much? I'm a data guy, so if there's a 10% increase in strength, I don't consider that significant. If it is 10x, then yes I am. Asking out of curiosity. Parts availability are not available direct to consumer, only accredited shops, unless you have a connection to such a shop and someone there willing to sell you. That's not an advantage to me.
I don't think you can say that. There's not much variety to regs. They do have some unique features, but so does Deep 6 (a "turbine piston"). Despite their uniqueness, one individual insists that they are copies of Apeks. I don't know how to convince this particular flat earther that the world is round. You may hear ScubaPro fanbois making this claim, but without the data of timeline of reg introductions and detailed analysis of the construction, such claims are farts in the wind.
Cheaper with equal performance means better return.
I can't say which regs do and do not have "second stage cases fiber reinforced." I haven't heard of that being an issue. That doesn't mean that an issue doesn't exist, just that I haven't read of any. My ears are open to anyone who can explain with real data.
I don't due to the oxygen percentage limit.
The trail to the Confluence in Canyonlands National Park is a famous spot for Jeeps tipping over due to the short wheelbase and tight turn (a longer wheelbase and making adjustments is allegedly the better way to go, like a Landrover Defender 90 - no personal experience as as I walked it as I was driving a non-trail rated SUV).
It isn't a bad product, but I'm not sure what you mean by "novel tech". I think the OP may have a defective one, and no product out there doesn't have some instances of defects, so can't knock ScubaPro for that. XDeep got screwed by an issue from a supplier for their regs with a tools issue. They didn't deserve the bashing they received for that.
But at $1100, that is stupid expensive. I'm all for paying for quality gear, but at some point the diminishing returns become zero. A crazy almost expensive Halcyon Eclipse is at $920, over 15% less. Is anyone going to claim that the ScubaPro is as durable as the Halcyon? GTFOOH. And I'm not Halycon fan. Good gear, but way too expensive.
For warm water diving, it is hard to beat an XDeep Ghost, which is less expensive than both. I regret selling mine as I'd have my wife or daughter use it one day.
In general, people are generally happy with the gear they have purchased, with rare exceptions. I've owned/own Deep 6 Signature, ScubaPro MK25 Evo / S600, Atomic M1, Apeks XTX50, and Aqualung. Anyone buying those brands is likely to be happy. Some might even claim that they are "the best".
But there is no best. There's easiest to service. There's lightest. There's strongest. There's can handle coldest water. There's all sorts of criteria/preferences that people have.
But the truly best regulators are on rebreathers!