This issue doesn't actually have anything to do with genuinely new tanks. They're generally upfront about their inexperience. I've seen this a couple of times in levelling dungeons and the entire group was supportive and encouraged sequential pulls, and this was on NA.

Usually the problem comes up with slightly more experienced tanks who have done all the instances before but aren't quite good enough to do a pull smoothly. There's usually a lot of jank around establishing aggro, and you can't ever tell how many packs they're going to pull. They wait for everyone to unload their cooldowns before wandering off, dragging the mobs out of the party's ground effect AoEs. Pulling more mobs or asking them to pull mobs will be seen as a personal affront, and they'll never admit to their inexperience. It's nothing to do with whether they 'can' do the pull or not.

The solution is not to engage in conversation, but just keep moving after the first pack is pulled, stopping just before the activation point of the second pack. There's no argument because they think that was their idea to pull that next pack. You can effectively shadow tank the instance this way.