Are Pop’gar and Rheastrasza Cuttable?

What are the purpose of cards like Rheastasza in Reno Druid and Pop’gar in Reno Warlock? Aren’t both of these cards too slow?

I don’t own Reno Druid and I have a slightly budgeted version of Reno Tick Tock Warlock without Pop’gar but I see that these two are included in every variation.

When you play Pop’gar on T5 you only get to use one Sludge and waiting until T6 to deal 8 damage seems mediocre? If I draw this against aggro I don’t necessarily stabilize since he himself doesn’t have lifesteal. Plus the decks have a heavy reliance on Shadow spells rather than Fel spells.

Rheastrasza is tutorable by the melon, but aside from that, is a dragon every turn actually that good? Seems like I’d rather end the game through Eonar or Astalor value instead of a random dragon every turn.

I’m willing to craft them if they turn out to be very good but I don’t want to spend dust on non-essential legendaries if I have to.

What are your personal insights on these cards having played them?