I think the main difference between bitcoin scripts and EVM/solidity is not turing-completeness but rather the fact that ethereum contracts can manintain states (i.e., they are statefull).

Bitcoin scripting langauge allows to use two stacks. Hence, for every fixed N, any function f:{1,…,N}->{1,…,N} is expressible with bitcoin scripts. So it has the same expressive power as computation circuits, which are often considered as turing complete.