the whole point of the lb penalty is in fact to discourage exactly what you are describing, taking unusual setups and especially double classes which is exactly why taking double classes get penalized, in the same way the 1% buff is an incentive to take at least 1 per role, these (de)buffs are in the game to counteract exactly what you are describing would never happen if they wouldn't exist.
in what way does taking a bard make it easier on the group than taking say a redmage ? if you say "troubadour" i raise (pun intendet) you a rezz, if you say "free movement" than again, in what way does this make it easier on the group ? the group doesnt care if its "easier" for the bard to play some movement mechanic, just that a)it gets done, and b) how much dps the class offers after doing it. all casters are perfectly capable of fullfilling criteria "a" with ease while domination the physical ranged in dps.
melee uptime strats that may be true (but still gets overblown), however as the bonus does exist (and its a completly different question if the bonus should exist at all/if the bonus should actually elevate the group dps or just be enough so dps stays about the same when taking a weaker dps class) this issue gets mitigated quite heavily, if phys ranged+melee did the exact same damage you would still take 1 melee for the buff.
the real question is would you take a second, at this point fight design would come in and how hard uptime strats are, if not doing them cost your one melee 500 dps while being of easy-medium level complexity to do it you would allready be doing them either way and most likely a second melee wouldn't add another layer of difficulty to performing them, if they were simply to hard to do/costing to little for not doing them thats in the end a fight design question and just means fights should be more varied in that regard playing to different classes strengths.
on the "difficulties of casters" again, what difficultys does taking a caster pose for the group ? not for the caster, the group. If it does pose difficulty for the caster okay, lets humor that thought, why play caster than ? oh yea, lets take your very own next words...
that exact reasoning can be applied to playing a caster, you play a caster instead of a physical ranged because you like the gameplay, you simply feel better going Explooooooosion instead of sending arrow after arrow into your enemy, YOU like the "challenge", you want the 300 extra dps you can get at the absolute top (thats the funny part, whenever someone says "phys ranged are x below casters/melee" they generally take somewhere in the 75-95 ranged, all casters/melee gain another 150-300 dps on the physical ranged just going from 95-99 and literally no one argues against that gap because everyone understands that this is needed as the absolute top gap otherwise phys ranged would dominate in the moment of slightest movement).
also, to go back to your original point on why you play nin, good on you ? no one ever denied you that, but you yourself said
the difference between nin and samurai (the highest melee) is HALF as big as the difference between bard and nin, not bard and the top, bard and the class you think is too weak,if only slightly, your "big whoop, i'm still outperforming them" is exactly the point, all you need to do is be slightly better than your competition, than you are top, like you being a 85% player while the rest is on the 75% level. to outperform literally anyone on a physical ranged is close to impossible no matter the fight unless the other guys suck so hard it isn't funny, the only "non physical ranged" realistically reachable is redmage, and that one is undertuned (yes, summoner is also simply overtuned but that doesn't mean redmage couldn't use another 400 dps on top of bringing summoner 300 down)
BRD outshnines the other physical ranged in ultimate for extremly fight specific reasons which are not likely (read, we didn't have something like this in 3 years or so) to translate into any other fight, and while i'm even in the boat of "find ways to nerf bards 2 target potency while getting up their single target power" even if its ultimate you should balance classes around an average of fights, not one in particular , otherwise you may aswell balance smn on e1s data alone for example.
i raid with pf, exclusively with party finder, yes people very much will get mad with you, and even if they do take you and are willing to make it work, mentallity wise whenever an average brd joins the thought process for everyone is "oh well, lets give it a try or two, but if its tight lets just replace him" whereas if a barely green summoner/Samurai joins its like "oh well, its a Smn/Sam, yea they suck ass but so what, they still do more than another phys ranged would offer.
Groups are happy when they get an average summoner and sigh when they get an average redmage, they may not kick you (and exclusions very much do happen allready) but as someone who does this shit with a different set of people every week let me tell you, yes people do get "mad" at you for playing the "wrong" class and the mentality very much is "take at least 2 ranges for mechanics. don't give a damn if you take take a second melee or an extra smn/blackmage,both work. never take a second physical ranged unless you are allready looking for half and hour and people start to get restless. if you absolutely have to take a second physical ranged make sure s/he is good, if you got 2 barely green physical ranged you don't need to pull". and yes, bad/average physical ranged get booted WAY faster than a bad top tier class.
the very best you may get out of getting a bard or whatever is a "oh well, at least hes a good bard" while bad bards get the boot half the time if they weren't excluded beforehand, the worst feelings a summoner will give the group are "well, at least he's a summoner" while "yeay, that guy is so great, we can die 5 times and still make it" is the top end.