I agree with the strategy, I never use glass canons because of the current bug in gyms makes them a team hazard. Gyarados is always a top pick of mine (not due to lack of viable Mon) solely due to his massive attack stat combined with reasonable bulk. HP hits hard into anything so I'd disagree with DonDon into Gyarados viability as an attacker just due to versatility combined with bulk. Vape is clearly a better pick for damaging anything weak to water, but like OP said Gyarados can attack most anything with B or DT then HP an incoming defender before potentially switching.
True my legacy Dragonites can rip through anything faster than Gyarados, but most of them are also sitting on gyms leaving Gyarados as a secondary generalist on my team.