Seconding this. If you spot El Dragon, call him out, because if he’s letting himself be seen it’s because he’s about to let loose on his nuke combo. Let your team know he’s coming in, make sure someone with a good CC is prepared and hanging back waiting for him to dive in.
They can CC him after his clothesline, which will give the player(s) he’s targeting a chance to escape or counter-attack, but ideally you want them to hit him with it AFTER his ultimate activates (basically right when he does the pose, don’t let him finish the pose or he may manage to pull off the Dragon Splash, and you can say goodbye to your butts). It does mean your teammates eat a chunk of AOE damage but if El Dragon is making his attack run solo (ie his teammates aren’t layering their own AOEs on top of him), it won’t be too bad. Most stuns will still leave him with some ult timer left afterwards, but with just a few seconds delay you’ve ruined his combo and likely put enough hurt on to make him run away. Even if you don’t manage to kill him in this time, now his ult is on cooldown and he will be back in harass mode for at least 60 seconds.
For this reason though, it’s more important than usual to control blind spots if El Dragon is around. He’ll always be looking for somewhere to clothesline in from unseen to initiate his combo precisely because it helps avoid being CC countered. So keep someone in the nest watching for him on Overgrowth, keep an eye on the minimap. He’s a lot more difficult to deal with on Capture and Meltdown as a result, as those modes have no real skirmish lines that force him back - he can run around pretty much anywhere he wants and attack from any angle.