Spine and Leav with BGP for overlay and underlay: at overlay level can I peer with border leafs only instead of peering with the spines?

Hi guys

I am looking at the design options for spine and leaf using BGP for overlay and for underlay.
The Spines are all in one AS and the leaves are all in one AS. We are using allowas-in and we peer all the leaves with the spines
A colleague of mine told me that instead of peering with all the spines (let's say we have 4 of them at the moment) we could peer all the leaves with the border leaves and have dumb inexpensive spines that don't have to support BGP EVPN

Do you see any drawback with this design?