You are probably going to feel the downgrade from the iPhone or the Note 9. I see reviewers still go with the S9 as the best flagship to buy today as a medium priced device as the prices has fallen a lot. I really like the P30 Lite. When I compare the P30 Lite to the Samsung S10 the P30 lite feels so much nicer. Battery lasts longer and finger print sensor is so much more snappier but then the S10 has such a better screen, double the memory and flagship features like water resistance ect.
If I'm forced to choose between the S10 vs P30 Lite I will go for the S10 but when I'm talking money then maybe the S10 is not that worth it unless the camera means a lot to me or the flagship features.
That said owning both devices when I leave the home in the morning I do tend to want to reach for the Huawei P30 Lite.
Honestly it really depends but I think you will feel you downgraded. If you can go to the mall and play with P30 Lite in a Vodacom or MTN store and see how you find it before you make the decision.