Plain and simple.

It's all about effort, and right now a JV girls team would show more than the heat.

This is so boring, but the Heat's D woes can basically be boiled down to a lack of effort. Not much else to say.
Some can blame the coach(not his fault), some can blame the lack of size(not the issue), some can blame the new guys(not the reason)

when this team decides to play with effort for the whole game, and it will come eventually, we will see a championship team.