@Staka~ Fearow has better STAB moves, no one will argue that it doesn't. However, Crobat's value isn't just in sweeping. It's also a very reliable status inducer and trapper, getting access to poison moves, Confuse Ray, and Mean Look. This (plus its immunity to Toxic) allows it to shut down annoying bulky wall pokemon (a.k.a. Toxic Stallers, etc.) without letting the opponent switch. It's also bulkier and faster than Fearow as well, with its 130 base speed stat. Plus, if you can manage to baton pass it a swords dance or two, Crobat can wreck opposing teams.
Bottom line, Crobat has way better utility and longevity than Fearow ever could have. Fearow has base stats of 65, 65, and 61 in HP, DEF, and SPDEF respectively. By comparison, Crobat has 85 base HP, 80 base DEF, and 80 base SDEF. This doesn't sound like much of a difference, but with its already impressive base SPD of 130 vs Fearow's base SPD of 100, Crobat is able to outspeed MANY more pokemon than Fearow can and get statuses onto the opposing pokemon before they have a chance to attack. Heck, that +30 speed doesn't sound like much, but that's enough to outspeed Alakazam and OHKO it, whereas Fearow would be the one getting outsped and OHKO'ed in that matchup.
Plus, with Crobat's added bulk that Fearow doesn't have, it's more likely to survive a hit (in general) than Fearow is. Oh and their attack stats are identical (90). Less powerful STAB moves are a small price to pay for such improvements stat-wise.
Crobat is EXTREMELY useful for all kinds of roles, whereas Fearow is pigeon-holed into the role of glass-cannon physical attacker. There are too many pokemon that can outspeed and OHKO Fearow that wouldn't be able to do that to Crobat. I like Fearow, don't get me wrong. It's just too fragile and too much of a one trick pony for me to use it seriously.
My best move-set for Crobat in Gen-2 would be my wall-breaking set:
Toxic (For breaking down stall/wall pokemon)
Fly (for STAB)
Confuse Ray/Double Team/Sludge Bomb depending on strategy
Mean Look (For trapping stallers/walls)
I've lost count of how many opponents I've faced in game and in human-vs-human matchups that Crobat has saved me in. I especially love how it HARD counters that stinking Blissey Stall/Wall set that was dominating the Meta back in Gen-2. Basically, when you saw Blissey come out, all you had to do was switch in Crobat and use Mean Look. Take Blissey's first attack like a champ then use Toxic. Once Blissey is poisoned, use double team until your evasion is maxed, preferrably having a sitrus/gold berry for HP recovery if need be. By the time Blissey lands a blow, the toxic damage will have increased to at least 50% of its health every turn and it won't be long before it's eating dirt. Then you can start finishing it off with Fly. Once your opponent moves on to the next pokemon, they're going to have a hard time hitting Crobat because of all the evasion stat boosts, unless they have Swift or something like that that doesn't ever miss. I've swept ENTIRE teams with that set.
But even if you don't take into account competitive battling, Crobat's utility, bulk, and better stats (both offensive and defensive) make it a better option than Fearow.