gyrados vs vaporeon

Vaporeon did his job during his time! Earned lots of coins! Did a lot of fights!

I think Gyarados and Vaporeon are 2 different water mon and you make no mistake power up Vaporeons.
Gyarados trade bulk with higher attack stat so Vaporeon fits into the tanky role while Gyarados offers more firepower.
Vaporeon also has access to Aqua Tail, a good multi-bar charge move which offer both power and maneuverability.
Not to mention Gyarados double vulnerable to electricity attack. Though Gyarados take neutral damage from grass attack.
All in all, both Gyarados and Vaporeon have their merits so your stardust is not wasted.

No reason to be pissed. Vaporeon dominated for a long time and was well worth the investment. My best one has over 4000 battles won, and sat in the top of a level 10 gym earning coins for 4 months. I’d gladly invest all that stardust in him again. Paid off many times over. I’m the opposite if pissed. He was a great investment.

You will have to sim to be sure, but I wouldn't be surprised if your gyarados isn't already on par with those vaporeons from a dps standpoint. From a TDO perspective, the two mon are now pretty similar based on the few sims I have run. I took a year off from the game so I don't have many powered up, but I have 2 vaporeon at 30.5 2692/2683 with solid IVs both WG/HP. I now have two Gyarados with weaker IVs but at level 32 both with W/HP and the Gyarados crush the Vaporeons on both golem and Ninetales sims. On Ninetales, its a 27s difference in time to win which is essentially a measure of dps: 185s vs 212s.

So unfortunately it looks like a pretty big difference.

I have both. Vapo is one of my strongest pokemon. It has high attack and med defense. It has very high HP and makes it like a tank. My Vapo's moves are WG/AT. Very fast attack move. AT is good at both attack and denfense too. 3100 CP is a nice value. You don't have to regret.

No really need to invest in level 30 Mons anymore when you can pick them directly at lev 34-35 with the right weather. Many mons invested in from lower levels to level 30 are going to be transferred in the long run

Vaporeon is one of the investments I never regret. Has fulfilled his role with pride.

Based on your situation, you should have some high level gyaradis from the pre-gym rework area available. You can simply TM them

No need to regret. I think Gyrados could not completely replace Vaporeon. As Watergun is much faster than Waterfall and it charges also relatively faster, some might find Vaporeon agiler than Gyrados, which may actually suit many people's playstyle better.

What on Earth did you need FOUR L38 Vapes for? That's a lesson in unnecessary redundancy, not changing Gyarados moves...

Vaporeon is still the best STAB WG/HP user overall.