Is scaling Bitcoin heading it to a dead end?
You're confusing different things here.

Parties incentivized to verify transactions are those that receive payments. Miners are only incentivized to do Proof of Work. (Although they have to be careful to not include invalid transactions while doing so.)

Mining is actually very profitable now. You can tell by looking at how fast the hashrate keeps growing. In the long term though, profitability is supposed to be near 0 because of competition: if there's free money to be collected, it would be weird if nobody came around to take it. Those who have cheap electricity inherently have an advantage.

Scaling solutions don't have much to do with any of this, other than possibly hurting the entire system by having blocks become too big. Scaling implies more transactions per block so which means, all things equal, more total fees for miners. Of course not all things are equal in practice, but assuming enough demand to fill blocks, a new equilibrium will be achieved.