Lightsail Vs EC2

From Lightsail FAQs:

Q: How do Lightsail instances perform?

Lightsail instances are specifically engineered by AWS for web servers, developer environments, and small database use cases. Such workloads don't use the full CPU often or consistently, but occasionally need a performance burst. Lightsail uses burstable performance instances that provide a baseline level of CPU performance with the additional ability to burst above the baseline. This design enables you to get the performance you need, when you need it, while protecting you from the variable performance or other common side effects that you might typically experience from over-subscription in other environments. For more information on burstable performance, go here.

If you need highly configurable environments and instances with consistently high CPU performance for applications such as video encoding or HPC applications, we recommend you use Amazon EC2.

They can upgrade to EC2 if they need more options later;

Upgrading to EC2 allows you to run your application on a wider set of instance types, ranging from virtual machines with more CPU power, memory, and networking capabilities, to specialized or accelerated instances with FPGAs and GPUs. In addition, EC2 performs less automatic management and set-up, allowing you more control over how you configure your cloud environment, such as your VPC.