Weir = unique player w/rare appreciation and extraordinary ear for harmony, physical good fortune of huge hands conspire w/harmonic gift to enable his fearless, adventurous sensibility to discover/invent all those never-before-played (and sometimes never again) voicings, leading notes, 9ths, 11ths, 13ths, flatted fifths, etc, previous posters have mentioned. More a picker that a strummer, very unusual for a "rhythm" guy, that may have been his "chair" but actually something of a mischaracterization IMO.
All of which made him perfect foil for Gar, first and foremost a melody guy, and vice versa. No GD w/out both. Have heard it said GD was collection of lead players, def merit to that point of view. Suspect, though, that Weir's "lead" playing wouldn't really carry the day, except maybe in jazz setting; little evidence of requisite melodic sensibility. Never should've touched a slide, IMO.
And yeah, tone lamentable at times over the years, especially on that horrid plinky Ibanez (ca. late '70s-early '80s), long as he was playin that I'd have buried him in the mix too. (Not knocking Ibanez - Strat guy here but have mid-'80s Ibanez semi-hollow w/surprisingly hot orig pickups that I rather like.)