Re-creating my client website

my client has this website that stresses me out. I think this site was created late in 2018. It is created by bootstrap 3 framework in a PHP file. And it was created by a guy in India. I live in UK and now help my client site by updating it etc. however, the guy has made it hard for me to understand what he was trying to do with the site, it’s very hard for me to create sections on the site without it looking bad. for example, I don’t know how this has happened, but the site has a video, which plays at the start. It is good on the desktop view but on a mobile device, the video has moved up? I don’t know what has caused this. also, the site is very slow now. I’m tempted to re-create this site, the way it looks now but instead of it being in a bootstrap 3 framework version, update it by bootstrap 4 or even by CSS grid etc. is this a good idea? is it worth saying or making up an excuse that site needs to be updated every 1 or 2 years?

Be careful, because it’s a big job to do that; it’s all a trade-off, and you need to decide whether it’s worth your time financially. But if this is the site that you’ve posted about previously that takes a few minutes to load, there’s something seriously wrong with the way it was built: if you can put together an MVP that won’t take much time to build, you should be able to show the client that you can produce something that works a helluva lot better.