As what other people have said, yes you can still get purple and orange gear but you get more of it on Heresy and Damnation.
You have quite a few games under your belt, you should try some Heresy games! I’m aure you’re more than ready for it. Also Heresy games can net you Orange items as well, albeit somewhat rarely.
Like others said the reward tier is tied to mission difficulty and side objectives. If you do T5+ (Aurics / Maelstroms) you almost always get the best rarity even if you don’t do scriptures or grims. I’d guess maybe like 20-25% of my rewards are purple and the rest are gold and I’ve done those exclusively since the Aug patch #12 they came out. :>
That said, don’t expect good weapons tho. Every single reward is always at the very bottom of my list. They’re a good way to get blessings but if you want actually good gear you need to buy/craft them yourself.
The most important part is that getting a legendary from a level 5, or auric mission means that you have a chance of having an emperor’s gift grant you level 4 blessings to consume.
If you wan’t to increase the chance, go for high difficulty and get all possible tomes/grims, that seems to increase the chance.
Frankly, they are quite often “meh”, majority of Emperors Gifts I got were guns with 300-320 power and level III blessings. Better than nothing I guess.