Sounds like you have some issues with your setting in lscache.
We are using it on a LOT of sites and have never had an issue with WebP images not being created if you have requested a domain key and have everything set right.
Personally on a LiteSpeed server I would always go for lscache but there must be some reasons why it is not working for you, I would want to troubleshoot it than jump to another solution, but if WPRocket is giving you the speeds you are looking for then maybe it’s a good solution.
I wouldn’t use any optimiser, just make sure that the theme and any plugins are well coded and use the optimise settings in the lscache plugin - be careful with the css and js optimisation settings, change - check, change - check, because you can end up making things worse rather than better.
When it comes to image optimisation, the one built in to lscache is as good as most of the others that are free, and shortpixel is, in my opinion, the very best of the paid options.