I think ENY should be harsher, BUT it should have a max value.
As a Knight player - we are usually outnumbered by big numbers of rooks and bish and we get steamrolled fairly often. If I look at a country's ENY, its usually below 8 or 9, meaning the high-numbered country is losing perked planes, spixteens, la7s, P-47Ns and P-51Ds. That's not severe enough with the numbers I have seen lately (i.e. 90 Knits, 140 bish, 130 rooks).
But I also think there should be a limit to the max ENY that can be imposed, say 19 or maybe 24. Something that still allows a good number of capable planes, versus "wtf I can only fly Hurri 1s, Stukas and Bettys?!?!?!"
Uncapturable fields = GOOD IDEA.
Dumb ppl who try to take them ayway = FUNNY.