IaaS lockin should be minimal if you make the right investments in automation and think hard about dependencies you can't unwind quickly. An IaaS deployment without automation misses the point of cloud. The easy test is "can you turn it off and get it back on without manual effort?" If the answer is no you are likely locked in. This would also be true in a colo or datacenter. The biggest benefit to IaaS is that you can make changes with reduced risk. You move away from 3 year cycles and big upfront commitments in exchange for the ability to make big changes quickly. If you move to the cloud and don't get that benefit you have not gained the core value. If you don't need that benefit you may not need IaaS cloud.
I have seen many cloud moves that don't leverage autoscaling and I've been wondering why anyone bothered. Is this just an inability to justify investing in modernization? Is lift/shift first a good strategy, it seems to me you miss the opportunity to fix long term tech debt if you just move.