So, I'm going down this path to discern which system to invest in and build toward.

In doing so, I'm finding some of the upper echelon systems using "built in reflectors" that have say a 77 degree output. I'm curious @ why the built in ... i.e. it seems restrictive to the ability to use bare bulb or spread wider than the built in allows for.

I realize that the upper echelon engineers didn't do this without any rationale ... I'm just wondering how they are intended to contend with applications wider than the built in.

Thoughts

This question has got to be the reason that Profoto doesn't mention that number much anymore.

It has an internal reflector because it has an internal flashtube. The designation of that reflector is immaterial; what matters is the beam angle of the light the whole unit produces, and that's a whole heck of a lot wider than 77°. For a point of reference, a Zoom Reflector set to its widest—a 105° beam angle—will visibly and significantly reduce the beam angle of the D1. (It will also increase the efficiency.) The reflector's there to serve the same purpose as the reflectors on Elinchrom products and the Broncolor Picolite: to push the light forward instead of wasting it.

Think of putting a flashtube at the bottom of a soup can. When you pop one off, most of your light's going to the sides and back, not out the front. You can solve that one of two ways. You can either add a reflector at a cost of effectively nothing, or you can add more capacitors and a beefier flashtube, at a cost of price, heat, power consumption, size, weight, and speed. And in the D1's case it's more like a tuna can. It's recessed just enough not to get smashed, so there's very little to obstruct the light.

Where the stock D1 may not be ideal in some situations is with modifiers like beauty dishes, and even that's largely a personal preference issue. If you slap on a beauty dish and don't like the way it looks, you can swap the frosted plate for a frosted dome and end up with a head with output as similar to any other Profoto head as any other Profoto head is.

So where's the 77° come from? Heck if I know. Even run totally bare with no plate, the output's much wider than that. The best I can give you is that the reflector surface itself is physically around 80 degrees, so maybe they're basing it on that instead of actual light output.

You refer to Profoto's D1 or Broncolor's Picolight, I suppose. In this case the mfgs consider them "travel friendly", on location flashes, the accent on small form factor. Both mfgs offer in parallel common (bare tube) pack&head units. It was their design decision (which I wouldn't follow in the case of the D1, btw).
So, which brand to invest in? You will likely already have made up your mind about 1) max. power per flash you'll need, 2) monolights or packs, 3) working single or with (freelance) assistants and so on.
For me, an important deciding factor is the service/ repair facility. Here in Germany (or UK), Bowens or Hensel are a no-brainers as repairs or replacements are readily available. In the US it may be a different case.
Next I'd factor in price / value. Unless I'm cashing extremely high day rates I'd be hard pressed to invest in all-Profoto or Bron (better to rent).
Finally, if I were US based I'd look for mfgs as Speedotron, Norman (esp. packs) or in case of monolights for PaulC (Einstein) Buff. The latter especially for a reassuring service.

Sure ... I get reflectors focus light to improve their efficiency at delivering light to a focused area. I just don't get why the restriction vs. where other mfr's use interchangeable reflectors that also afford the option to use bare bulb.

Yes, the 77 came from Profoto D1 series.

You mention the "frosted dome" vs. the "frosted plate". Is it their option to use a "frosted dome" that generates a wider dispersion of light beyond the restriction of the built in reflector? Thereby, emulating a bare bulb dispersion, but with a more diffuse output rather than the specularity of bare bulb. If so, then the built in reflector is no longer restrictive as it might seem to be on spec.

As Peter alluded to, the decision to go internal with the flashtube was because Profoto found their monolights were heavy travelers. Moving the tube into the housing offers some protection both in transit and on location, especially compared to the ComPact line the D1 line replaces.

For the D1s, there's an optional frosted glass dome (in two or three K temperatures) you can swap in for the standard frosted glass plate. Every other Profoto strobe ships with a frosted glass dome as standard equipment.

Truly bare naked bulb isn't much of a consideration in Profoto's product lineup; they offer token optional clear covers which nobody uses, but you're intended to use the frosted ones everything ships with. Conversely, Broncolor ships everything with clear covers and offers token frosted covers which nobody uses, leading to much of the old hullabaloo about Broncolor being edgy and clinical and fashion while Profoto is warm and pleasant and portraiture.

Thanks guys ... that is helpful info.

Always a preference to objective info that explains differing opinion. Somebody saying Broncolor is "better" or Profoto is "better" is an opinion. Explaining how they are designed and objectively engineered works "better" for me.

Of course, following objectivity with subjective opinion isn't all bad. I just find that opinion without objective explanation doesn't help me grow my understanding or decision making process.

Thanks again.

BTW ... if Bowens is now being mfr'd in China ... have they changed where their repair facilities are located also?