We shoot wedding videos professionally and use the 55-250mm STM everytime. STM lenses work great with the Canon 70D’s focusing.
That said… yeah, they’re not a high quality lens. We use them to pair the STM with the long reach during the ceremony and don’t use them the rest of the day.
And I’ll chip in and say the same for the T5: Don’t buy it. Go buy a used T3i if you’re on a budget.