The final decision to select Polec was only made a few days out from draft, Kerr said.
Heppell, 18, had been consistently linked to the Lions at pick No.5 but late mail on Wednesday suggested the club was leaning towards Polec, who had been tipped to go to Richmond or Gold Coast with selection No.6 or No.7.
Kerr said the Lions recruiting team had made a relatively late call to take Polec after taking a good hard look at their future needs.
"It was a real toss up between Dyson and Jared," Kerr told afl.com.au.
"When we had a hard look at our list and looked at what we needed the most, Jared was probably the best fit of the group in terms of the players that were going to be available.
"Dyson is a terrific player and will have a fantastic career. We just thought from a pure list management perspective that Jared fitted our needs just a little better.
"Jared is going to be able to provide us with plenty of run and carry and really add something to our line up."
Polec has had plenty of experience at senior level, having made his debut for SANFL side Woodville-West Torrens as a 16-year-old.
The dashing onballer starred during the Eagles' finals campaign this season and was named All Australian at the NAB AFL Under-18 Championships in June.
Lions coach Michael Voss said he was pleased to add another left footer to the side, which already includes former NAB Rising Star winner Daniel Rich and skilful half-back Josh Drummond.
"We won't be playing down the right-hand side of the ground at all. We'll be playing left-hand side the whole time, which will suit Browny [skipper Jonathan Brown] quite a lot because he doesn't mind swinging around on his right when he's having a shot at goal," Voss joked.
"We've got a few left footers now. Drummo [Josh Drummond] and Daniel Rich are probably the two of the best kicks in the AFL. I'm sure Jared will have his work cut out keeping up with those two, but if he can get to that level he'll be pretty happy and so will I."
Polec said he wasn't fazed about moving interstate away from his friends and family, which includes twin brother Daniel, and that he was hopeful his senior football experience would help him slot straight in at AFL level.
"It's a massive thrill just to be here. Being drafted is great…but I don't just want to be a number, so you've really got to do the work now and this is where it all starts," Polec said.
"I'm a bit skinny, so I want to put a bit of weight on and hopefully get through the pre-season and come into the NAB Cup. I've played against some current and some ex-AFL players in the SANFL, so it's been a good experience to have coming into this level."
