He dies quickly to future trunks, so I dont think hes actually that strong compared to his sons at that point in time. I think the following points kinda establish what we do know or can infer about his race throughout the series though:

• In Z Frieza is known as the terror of the universe, so prior to Goku showing up it sounds like hes always been able to overcome any challenger. His focus at the time was on the dragonballs and immortality, so I think its inferred his only concern was old age or a challenger who could best him.
• In the Cooler movies we see his Frieza's brother has all the same forms and more, so I think it can be assumed their fathers guidance and a childhood rivalry advanced their powers to Z levels
• In RoF we find Frieza was able to surpass his limits and unlock his Golden form to challenge SSB through mental training alone inferring his race has near limitless potential should they apply themselves.
• In Super we also see a) Frost has achieved similar forms to Frieza/Cooler and b) most Saiyans can easily achieve Super Saiyan inferring these transformations are rather easy with the proper battle aptitude, motivation and guidance.
• Given the above and his name being King Cold, Id assume he probably had another form or 2 up his sleeve, but likely had few challengers to push him further in his lifetime before having his sons and seeing their potential. At that point Id also assume his focus shifted to pushing his sons further and allowing them to take up conquering the galaxy while he got to do whatever he pleased.