1. yes they serve a purpose: owners can charge a full price ticket to see practice football.
2. yes. You evaluate talent in practice (training camp.) you can also do joint practices with other teams, which everyone already does, and I have no problem with.
preseason games probably had their worth, way back in the day. Similar to your appendix. Now they suck and they’re horrible football and they’re are ONLY there so owners can get their home game gates in.