The end reward of the Dockyard Event is a Tier 9 ship, but you are correct that you must spend Doubloons in order to acquire it. Still, when creating the event the end prize must be weighed when evaluating the amount of effort that is required to attain it, discount or no.
The Dockyard doesn't have to be completed to get a host of rewards from all the stages which can be achieved just by playing the game.
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The Co-Op Compatibility Review is for making sure that everything can be done by a strictly Co-Op player. Operations are another PvE activity, but it has been pointed out correctly that there are players which only play in the Co-Op Mode while still wanting to take part in major content beats as well as side missions for flags and patches and other fun recognitions.
I'm assuming "he" is meaning me? To be honest, 2,300 Base XP is extrodinarily hard to achieve. It certainly can happen, even multiple times in a single night if someone is a remarkable player or having an amazing windfall of luck... but it's not something to expect. Challenge Missions like these have been included in the new format of Dockyards for the past as many current-style Dockyards as I can recall. They are not easy to do, but if you enjoy PvP and happen to complete one it can make the grind a calmer experience.
If you choose to use them, you can tally it like that. You could also perform the grind directly with no Premium Time and only using a Tech Tree ship with no Bonus Package, but it would certainly take quite some time.
It's not a bad idea to hold onto EcoBonuses for the times when you can get the most value out of having them. Being able to get the Commander XP that they offer while also completing a mission that leads to yet more rewards at the same time is a good way to make the most out of their assistance.
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As for the "getting 1800 bxp in coop is kind of hard isnt it?":
I don't think 1,800 Base XP is possible in Co-Op, though there may be a screenshot of someone doing it once? Co-Op's reward structure is lower than Random Battles or Operations, but the mode is consistant in the bots' willingness to give their lives for player rewards as well as a fast turnaround time. You can fit 2-3 Co-Op Matches into the time of a Random Battle, so the Base XP tallies up over time. EcoBonuses don't go as far in Co-Op due to the smaller Base XP earnings, but Operations is a mode which can pull above 1,000 Base XP rather routinely with opportunities to have games with notably high rewards. That's a PvE Option that is a better fit for use of EcoBonuses in terms of individual efficiency.
If you'd like to see me using Co-Op to complete an entire week's worth of a previous Dockyard event, you can find me doing a time-trial in a single streamed session here. Players requested that I do a grind with Tech Tree only, Tier 8 or lower (since many players don't have above Tier 8 ships), no bonuses/camos (I had Premium Time, but there's no way to turn that off).