Ethereum only runs at 15 transactions per second. If you want your App to run at 8 transactions per second then yes you are going to stress the network and see costs rise till people stop using it.
Ethereum's performance problems are well documented at this point, but using a more centralized blockchain like stellar is even more pointless in my opinion. Why not just use traditional platforms to build your application if you don't care about the decentralized nature of blockchain?
Because blockchain allows you to raise a large amount of money from unsophisticated investors without going through third parties who might ask awkward questions like "is this actually going to work" and "why are you incorporated in a non-extraditable jurisdiction"?
There is an argument for Plasma/State channels here though, where transaction speed and fees become an issue only when users cash in and out of a state channel? It works for some business models, not necessarily all. I just feel like the Ethereum community is aware of this, and moving in the right direction.
Ethereum only runs at 15 transactions per second. If you want your App to run at 8 transactions per second then yes you are going to stress the network and see costs rise till people stop using it.