I went to Mexico last year.
There's no problem with this one -- it' a simple statement!
I have been to Mexico in the last year.
This one is fine, but is asking to be extended in some way, with something possibly in the present or the future. For example,
I have been to Mexico in the last year, but don't think it's too soon to return. or
I have been to Mexico in the last year, so I am familiar with the current political situation.
I’d been to China last year.
This one needs some extension, but with something also in the past. For example,
I’d been to China last year, but I was happy to return earlier this year. or
I’d been to China last year, so I knew what to expect when I returned recently.