Maybe you shouldn't use the term platform in this context. It is miss leading, neither Steam nor Epic are platforms. PS4, PC or XBOX are platforms, the term platform in a IT context is used for Hardware (https://en.wikipedia.org/wiki/Computing_platform).
And there is a huge difference between Platform exclusivity and Shop exclusivity. In terms of games one prevents you to play it on any hardware you own (PC, PS4 etc.) when it was exclusivly released for another platform. The other "just" forces you to use a certain shop but you could still play without paying for new hardware if you used another shop before.
Both is exclusiv but with completly different consequences for you as gamer.
Borderlands 3 is a nice example for this, it's Epic exclusive but not platform exclusive. So if you own a PC you are forced to buy it at Epic but can still play, if you own a PS4 you also can still play.
Horizon Zero Dawn would be another nice one. It was platform exclusive for PS4 so there is no legal way you can play it on your PC, you can't even buy it for PC.
When you still say both is the same, then i really don't know whats going on in your head. Because for me both are completly different exclusivity deals, one of them makes me angry, the other just annoys me. Guess which one makes me angry.
Console Wars were fought with platform exclusive stuff, again completly different then the stuff happening with Epic and Steam. Basically the same, but hugely different consequences for a PC gamer. No one prevents you from playing anything, as it happened when Sony and Microsoft went to war with all their exclusive stuff.
Aerm you are not right.
Steam = the ultimativ online gaming platform - thats what steam says
Origin = platform packed with great PC Games - thats what EA says
Uplay = details for this plattform - thas what Ubisoft says
EPIC = the games you buy on this platform ......... - thats what EPIC says
PS4 and X-Box in the first place are hardware and at the second an console or an platform to game or interact with others.
PCs in the first place are Hardware and in the second an plattform to use different softwares.
Steam, Epic and the others are in first place an software and at the second an platform to buy, download and play games or interact with others.
The therm platform has an wide area of definitions.