I wouldn't call it a detriment. You don't have to use your moves off cooldown, being at 100% isn't always a detriment, and having a shorter cooldown on your ult is pretty nice too.
Except when you are in a teamfight with Rumble or chasing; the 6 second cooldown for Flamespitter is just right to keep it up without overheating yourself. Provided you stagger your Harpoons and are faster than your enemy you can chase fown a lot of champions like this and zone them from the wave. Standard procedure of Rumble is to activate Flamespitter off cooldown because you are chasing after people.
However cutting that period means when you are doing this you just overheat yourself. It plays against the
habits and comfort zone of Rumble and makes heat management
more difficult. And it's not just Flamepsitter. Your Shield and Harpoons are off cooldown faster as well; and you want to use those off cooldown to chase too.
Also The Equalizer's cooldown is generally good enough as it is except sometimes at Rank 1.
Also the way I like to use Rumble in teamfights or all-ins is weaving in and out. I go forward while Flamespitter is on; and back off to minimise damage when it's off. CDR disrupts my flow.
CDR on Rumble makes heat management harder and disrupts the general play patterns of Rumble. I play Rumble enough that my pattern of weaveing in and out with Flamespitters is almost second nature as it comes off C/D. I feel notably disrupted when I have Blue. That's why I consider blue a detriment to Rumble. If blue made his heat cooldown faster I'd actually be fine with it since it lets his rhythm stay the same. It would also probobly be stupidly OP.
Blue doesn't
hurt Yasuo or disrupt his gameflow; and helps two of his skills; not one.I'm a massive speaker for the importance of CDR.
I'll even get CDR boots on champions like Sivir some games [Her base AS is awful anyway and CDR boots lets her use Richochet more often and generally gives her MORE DPS than Zerkers]. On most mages I'll get 40% CDR; even if it's not normal [EG: I play Ahri more as a kite/poke champion than an assassin]. I love champions with a 'CDR overclock' mechanic like Karma. But on Rumble? I keep from CDR like the plague.
I guess it's less of an issue for Eym or other really; really; really high level Rumble players, but for me? I hate getting blue. And I do consider myself above average as Rumble.
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STOP GIVING COP CORKI.
Also why is it every time I see Cop doing well it's on an ADC starting with C? [Caitlyn or Corki]