Heyo Grimmortals,
We have no made any major changes in the way EXP/Credits gets rewarded to ships for actions in a considerable time. Therefore, at least from our end we cannot correlate that to the way in which DDs are choosing to conduct their gameplay. In the last year or two we have seen an increase in ships with the ability to hamper DDs from preforming these functions (yes, I'm talking about Radar) but have consequently balanced this with changes made to Radar (6 second delay for enemy spotting). There is EXP/Credits rewarded for capturing and defending caps:
Full Capture:
EXP = 2/3rd of killing a ship
Credits = 1/3rd of killing a ship
Shared Capture/Defense:
EXP = % of capture/defense X 2/3rd of killing a ship
Credits = % of capture/defense X 1/3rd of killing a ship
While it is hard to force another player to play the game you expect it to be played based on class rolls, you do have the ability to play with friends in a division to ensure a better chance of having capable support in your DD actions.
In your last point, 50k dmg to a BB should equal 10k dmg to a DD, this in fact is the case, however it is based on %s rather than strict damage numbers.
For example, a 105,800 HP GK and a 19,400 HP Gearing.
Doing 50k dmg to the GK would be 47% of its total HP
47% of the total HP of the Gearing is 9,118 DMG5
50k DMG on the GK equals the same reward as doing 9,118 DMG to a Gearing
There is a great How it Works video on the matter if you have further curiosities on how this works:
Fem,