Hubspot cms

I have asked previously about HubSpot and migrating the existing website to the hubspot cms. What’s attracting my client is the fact that - It’s simpler to design, the drag and drop builder can help us achieve our targets. We can buy a theme and use it to design the website easily without dev support. Price isn’t a worry, they are happy to pay the ongoing fee. I have heard hubspot isn’t scalable or flexible, seo recommendations are hard to implement, we can get locked in and it’s hard to change the platform. Why is Hubspot not scalable or flexible and why are the seo recommendations hard to implement? still not convinced with Hubspot and it’s functionalities and unable to convince my colleagues with not to switch there. Is there anything you could point out that could help me so they change their mind and don’t switch to Hubspot.