Is English a language most of us will not be able to truly master?

English is one of the primary languages used in my country. However a lot of us are not proficient in it. I struggle when I have to say/write something like these:

Example 1

The phone I bought last year is more expensive than this phone.

or

The phone I bought last year was more expensive than this phone.

You see, the former phone IS still more expensive but since I am describing something in the past, it feels like Was is more appropriate. How do I tell which to use?

Example 2:

Chopped almonds is my favorite ice cream topping.

or

Chopped almonds are my favorite ice cream topping.

Here I am trying to say which topping is my favorite, which is why I believe Chopped almonds is... sounds correct. However chopped almonds are plural noun hence it feels like chopped almonds are... is more appropriate. Do you see why this is difficult for me?

I ve tried to better my English via external courses but I still couldn t grasp a lot of the rules and exceptions.

Is English a language most of us will not be able to truly master in our lives? Should we ignore grammar nazis when they pick at us in informal forums and chats?