I'd be inclined to disagree.
Gnomes have undergone a decline in the 'seriousness' of them as a sensible race. Gnomes are beginning to decline to a sort of 'comic relief' type race, particular in the context of popular fantasy movies- even dwarves were undermined as a serious race in the LOTR: Two Towers movie.
The gnomish bard is the final nail in the coffin, and misunderstands the whole gnomish ethos. Someone mentioned the left-brain/right-brain divide when I posted this on another thread.
Examining the gnomish description from the PHB:
'Gnomes are welcome everywhere as technicians, alchemists and inventors'.
'they apply the same dedication to more practical arts, such as engineering'
'share...their curiosity about mechanical devices'
'Gnomes who settle in human lands are commonly gemcutters, mechanics, sages or tutors'.
Do we see a common thread? Gnomes go for practical, material and mechanical arts, and whilst pranksters, prefer sciences to arts. Whilst they no doubt welcome bards, they do not incline towards them. What's their dominant alignment in the law-chaos axis? Neutral. So having a favoured class with a non-lawful alignment is bizarre. The MM underlines the notion of the scientific, mechanical orientated gnome: 'skilled engineers', 'practical experience'. They are culturally empirical and scientific, not abstract and artistic.
The argument that 'well, elves are wizards, so gnomes can't be a subset of wizards' is nonsense. Why not let gnomes become wizards, fitting with the notion of empirical practical learning and an emphasis on knowledge, and let elves take bardic favoured class?
Consider the elven description in the PHB:
'They are well known for their poetry, dance, song, lore and magical arts'.
'skill with sword, bow and battle strategy'
'love freedom, variety and self-expression. They lean strongly towards...chaos'
'Elves encountered in human lands are commonly wandering minstrels, favoured artists, or sages'
Indeed, the elven description is almost archetypal of a bardic character concept. They lean towards chaos (appropriate for a non-lawful class), are driven by wanderlust, have some martial weapon proficiency, a high cultural emphasis on a combination of the fine arts, magic, and swordplay/archery. Which classes do we know that combine art, magic and some magical prowess? I'll give a clue- not the wizard.
The point is that the gnomish bard and elven wizard set up a fundamental contradiction within the cultural emphases and the mechanical emphases between the races. It's the old problem of the crunch not matching the fluff. Sure, you can just about justify gnomish bards and elven wizards in the way you can't justify ogre diviners, but it makes far more logical sense given their self-defined culture to make make gnomes have a wizardly favoured class, and elves a bardic one.
End of rant- thanks for reading
