I'll just state my opinion on why these thermal clips don't make sense.
So, we technically still have infinite ammunition. But we don't. But we do. But we don't. They now use the forsaken ''numbers'' thing, as for the ''magazine'' (which doesn't exist) and as for the ''ammunition'' that's left (which also doesn't exist). Enough of that, here's what I mean:
You would swear the gun would cool off on it's own. The ''heat sinks'' aren't truly doing their job. Their point would be to absorb the heat so the gun doesn't malfunction, right? Yes. But think with me for a second: wouldn't the heat sink cool off, since it's a heat sink?
I mean, even nowadays we are technically more advanced than this future that BioWare wants us to believe in, if the problem is truly the heat generation. Nowadays, some old (almost exclusively) machine-guns that were supposed to shoot loads and loads of bullets can heat up. Guess what happens. No, they don't ''eject a thermal clip'', they leave the gun for a tad, and it cools on its own. Simple.
How I think they should have done it: keep the bar that fills up, but have a limited number of thermal clips. The player should make the choice of letting the gun cool off, or ejecting a clip, cooling it instantly. This would, in fact, be an improvement over the original, and would provide the sustained fire they wanted.