What is wrong with the use of some modern, simple past and present in the following sentences?

Quality of air in southern Ontario is the lowest since 1990.

Yesterday was the first Free concert of them in New Zealand in 2013 (also their 3rd concert in the US): the first acoustic performance since 2003.

Why are there no cleft sentences?

At 2:00pm they played their first free online concert since 2003.

Is my understanding correct? If not how could we justify this usage of since with a tense other than the present perfect?

What are some practical tips for the UI job-student to learn to perform independently?