For a start I would suggest a Firestick rather than a Roku, I've got both - and not used the Roku for years, as the Firestick is far superior.
But TV's aren't 'smart' no matter what the manufacturers claim, and a Firestick is far 'smarter' than any 'smart' TV - but if the TV does everything you want (and you won't know because you can't see what you're missing), then stick with that, until the in-built apps stop working.
It's not usually a question of the apps failing, it's the broadcasters - YouTube for example closed large numbers of their services, and this stopped YouTube working on thousands of TV's. Watching YouTube (or any other app based chanel) on a TV isn't the same as doing so on a computer, they use special limited versions of the content for TV's, and are frequently closed by the broadcaster to save money.
The BBC iPlayer apparently had hundreds of different services, and when they closed a few dozen of them huge numbers of TV's lost the iPlayer service, as happened when YouTube did the same, as happened when ITV did the same etc, etc, etc.
A 'smart' TV is usually a short term device, and gradually becomes less and less 'smart' as services close - a Firestick is far more powerful, and MUCH, MUCH more likely to keep working, as they usually use the 'full' services, and not the cut-down special TV services.
But if you're happy with what you've got?, just don't look what you're missing, and you'll stay happy
Wait until you start losing services, then buy a Firestick (or Roku).