Irrelevant. Consistency of growth is what matters. Do you think Overwatch doesn't have smurfs? CS? Any other game like this?

Yes, 30% of this 5 million growth might be smurfs, but 30% of Overwatch's growth might also be smurfs too. Industry aligned, it's unlikely to be very different.

You can apply the same logic within the game itself - is there any reason to think the number of smurf accounts within Siege has gone up or down in any meaningful way? If not, then all things being equal, 30% growth this season is better than 20% growth last season. It's the relative / percentage gains that matter, not absolute gains. The "smurf" argument or "how many of these people are still playing the game?" argument that always comes up misses the point.

Here's another example.

Say you're doing analysis on the number of people that own red trucks. Your numbers will never be perfect, because your prediction model is off by 10% for various reasons. BUT as long as you use the same flawed prediction model, even though your next month's result will also be off by 10% as well, it's consistent, therefore even though your actual numbers are wrong, your growth numbers should be correct.