The Q3 Gauntlet is already more powerful than the Doom chainsaw. 2 lovetaps from it will force most anything to respawn soon afterwards. (Doubt me? I'll show you on a server - just ask)
Each has their ups and downs, but the guantlet does 50 damage per slap, while the saw has a slightly longer range and 'sticks'. I'd put them about equal in strength.
It's not fun to play against something which is near-impossible to counter, even if the user of that something is inept. It's even worse in the hands of someone proficent. This is why many Q3 servers have the BFG filtered out or don't play maps/mods with the BFG in it.
The BFG is much more prevalent in Gen than in standard Q3. EVERY map has the potential to have a BFG, if the earth guy drops dual gats.
The Doom BFG has its counter - don't be in the line of sight of the user or kill them before they get the shot off. The Q2 BFG has a counter as well - kill user before it goes off or run away; the charging time for the BFG10K is longer than the BFG9000, and the shot is slower. This is why Q2dm8 got a lot of playing time on Q2 servers (aside from it being a really fun map in iteself) - because the BFG10K was acceptably balanced with the other Q2 weapons.
Their charge up times are the same, but the rest is true. Both weapons, while fully capable of clearing a room, require a bit of finesse. There are a LOT of people who simply cannot use the Doom BFG to good effect. The Q2 BFG is slightly easier to use, but it is also much easier to avoid. It's nearly impossible to be 'sneaky' with the q2BFG, unlike the Doom BFG.
The Q3 BFG is like an automatic Q1 RL. Not fun. I'd like to see a fun, properly-themed replacement for it in Gen because imo it doesn't even belong in Q3.
We've resisted changes to the Arena class in the past. However, in 99d, we have recieved only two major complaints: The q1 RL is far too strong, and the q3BFG ruins the fun. Take a map like Dead Simple, which is a long-standing favorite in Doom, and is probably the single most-remade map out there. This map includes a BFG. I usually sit out in this map if there's ANYONE playing as arena.
Why? Because the q3BFG just pisses me off. I hate it. There's no way to avoid it. If someone's halfway skilled, you die. If they're not, you'll still likely die. I can at least duck out of the way of the BFG9000 or hide from the BFG10k from Q2. And I've heard lots of complaints about this from other players as well...
In short, the q3BFG is cheap, spamtastic, and nearly impossible to avoid.