If you use S Pen and want to use the best out  of the best then is worth

go for the ultra. 

superior camera and functionality.   

think of it this way.  you invest in a better phone for long term usage. say 3~4 years.    is not like you are going to upgrade phone every year right. 

so go for the ultra. 

really worth it.

Yes, it really is worth the extra RM 800. You're getting a better screen, much better cameras, S-Pen functionality, slightly better battery life and the sizes are so similar you won't feel a difference holding/using it compared to the S21+.

Your options should really be either the S21 or S21 Ultra only. The Plus feels like a redundant device that offers nothing much when compared with the S21 and S21 ultra.

You pretty much summed it up.

The Ultra's screen is actually more power efficient than the S21+ as it has a VRR of 10 to 120 hz. If you're going to use it on FHD+, you'll see a much bigger battery improvement when compared to the S21+.

Then again, if cameras and stylus isn't something you need and you intend on using FHD+, there is no reason to consider the Ultra to begin with.

When the battery is the most important point, S21+ makes more sense.

obviously la ultra