Sites like that are great for simple ordering of matching parts, but they're much less useful for parts research. Sometimes things in the EPC aren't clear, or your model has had some upgrades, IE, you've swapped out various bits from other models. That's where the EPC is irreplaceable. I can put in my VIN and get all the same info as you get from partsouq or the like, but I can also turn off spec match, and see all variants of that part that were offered across all models and years of the same vehicle, across all trim models. That is absolutely invaluable when you're trying to figure out how to make something work when your rig isn't stock, or a part is NLA or unavailable. Maybe that trim part you want is NLA in black, but it's available in grey-blue? It's also the only way to really understand the subtle differences in each model over time. And again, searching parts applicability across models has saved my butt several times. If you're hunting an NLA part, but you happen to know it's the same part not just in your rig, but also a 90s corolla, you'll have a much easier time finding it.
Partsouq as you said is great for pricing and sanity checking with pictures. I also find amayama useful, as they explicitly state when they know parts are NLA/out of production, which most other places don't. I start with the EPC personally though, then go on to another site, unless I'm ordering something brain-dead like an oil filter.