So you are saying there is no advantage to having a bow which automatically adjusts to the user's strength score (by which I mean, it adds the user's strength modifier to damage) as opposed to a composite bow which only does so for a predetermined strength score?
No. I'm saying that you can profit from your FULL str with a simple composite bow without spending a feat for it.
Moreover, I'd keep in my Efficient Quiver (something any decent archer SHOULDN'T live without) a couple more composite longbows with the appropriate bonuses IN CASE my Str gets damaged, fatigued etc. Quite cheap, and still far better an investment than spending a feat.
Well, I guess if the archer just doesn't increase his strength you have a point, but I for one do not see increasing strength as a "waste of time". Archers need bonus damage to punch through DR and end fights quicker. A Rogue gets Sneak Attack, for example, and a Fighter uses his Strength.
I don't see what better one can get than a belt of Giant Str. That's a +4 or +6 enhancement bonus. And the composite bow should include the bonus damage. If the party's wizard, druid or other spellcaster invests in the archer's strength BEFORE the archer can get his hands on such a belt (meaning the early levels).... then they are simply doing something wrong.
And one more thing ->
I mentioned it earlier, but it seems it went unnoticed:
Bone Bow, Frostburn page 75:
The bow has a long, thickg spike protruding from both ends; this spike is used to brace against a solid object (either the ground or an overhanging protrusion or ceiling) to aid in pulling the bow's string.
What I gather from the above text (and the sketch on page 77), you need some sort of object to brace the spike against OR some sort of surface to stick the spike in, in order to use the bow properly.
Since this bow is found in Frostburn, my first thought was ice. You either stick in on the icy ground... or the icy ceiling above and then you can use it. Of course you can brace it against some object, (even if you are not on some frosty terrain) or even stick it in the soil, perhaps even in the sand... or whatever surface/object have you that can hold one of the two spikes.
Despite the above possibilities, there are plenty of surfaces you CAN'T use the bow with. Natural Rocky surfaces, tiles of all kinds
(both of which compose the majority of dungeons)... are enough to make my point...
And, last but not least, you can't shoot while air born. Even when you are not under the effect of the fly spell any beast you ride on should come with the appropriate equipment so as to hold the bottom spike (if that is even possible)...
Now Depending on how severe the DM is, INHO it comes down to two options:
1-If one of the two spikes isn't held fast by an appropriate object/surface you cannot use your bow at all.
or...
2-If one of the two spikes isn't held fast by an appropriate object/surface you cannot profit from STR while shooting the bow.
(This second options comes in many colors: a) No STR bonus b) No STR bonus & a -4 on the Attack Roll c) ..or just a -4 on Attack Rolls)
....I'd love a scene in the game where some northern barbarian clan is standing upon a frosty hill with their Bone Bows stuck in the ice and ready to fire down their opposition with bone piercing shots... that I'd love...
but an adventurer with such a bow? with all the variety of terrains he has to deal with? ....No I don't see that...
And it requires an entire Feat you say?
No thanks.