The convention is down where the stadiums are. Not much to destroy, not a friendly neighborhood to outsiders. The Philly perimeter does have to be secured on all four sides. A major issue will be the freeway just to the east. If the rioters wanted to do one of their freeway blockage ops and associated mayhem, they are a few hundred yards from the venue. If the protestors want to screw with convention goers at their hotels downtown, things might get a bit dicey.
Cleveland is a slightly different deal. The IX center is located at the airport, so it is locked down on three sides by airport, with one road access. The issue will be with convention goers staying downtown.
The problems in Philly will, as you say, be at the downtown hotels. They may try to sneak people onto the convention floor to try and draw attention to what’s going on outside the hall.