Yes, you did hit the nail on the head.
You will get asymmetry in the improved design, but asymmetry is a fact of life on the Internet, and there's really no good reason to expect symmetric routing of traffic to/from. Shoot, the whole concept of packet routing is that separate packets are routed independently of each other and may take different paths, even packets going in the same direction.
Personally, I loath PBR. Its one of those technologies that when I decide that its the best solution to the problem, I stop and take a step back to see if I really understand the real nature of the problem, even back to figuring out what the business problem to be solved is. When I do so, I almost always find that there is a way to solve the problem without using a technology like that.
Having full Internet routes in your routers will take some getting used to, but once you get used to it, it is indeed very easy to understand and troubleshoot. Certainly there are fewer "moving parts" of different protocols to worry about.
You don't want to have full Internet routes in your OSPF database, so you'll want to advertise a default via OSPF into the interior of your network (or perhaps static default...personally I prefer default in OSPF). That will move traffic towards the BGP speaking Internet routers which can make the more fully informed decision of having the full Internet routes.
That will give you close to "destination based best path". There will still be cases where the traffic will do things you don't quite expect, so you'll want to get familiar with the BGP route selection process.
I would ask for 'maximum-paths' (it's usually called ECMP in standards and documents, not ECLB). And if ECMP is non-starter, then fallback to your /25 plan.
Other acronyms that I couldn't immediately figure out were DIA (dedicated internet access?) and SOP (standard operating procedure?). I'm not sure if these are really so universal acronyms that they should be used in stackexchange without at least hovertext to resolve them.
Best Answer
BGP multipath is for load balancing, not fail-over. In your topology, a basic (default) BGP configuration will already fail-over to one of the ISP2 links if both ISP1 links are down. If you'd also like to load balance between both ISP1 links (or both ISP2) links, by all means also configure BGP multipath. But it has nothing to do with fail-over.
You might find this helpful: https://www.juniper.net/documentation/en_US/junos15.1/topics/concept/bgp-multipath-understanding.html