Roth IRA vs 401k in-plan Roth conversion

Hi all, long time lurker first time poster. I get a year-end bonus that puts me perilously and unpredictably close to the IRA MAGI limit. I used to auto-contribute every month to a Roth IRA, but a couple years ago my year-end bonus put me over the limit and I had to go through all of the paperwork to fix it at tax time. After that I switched to just doing the in-plan Roth conversion. * I'm maxing traditional 401k and HSA. * There are more investment options with the IRA admin, but the options with my 401k admin are sufficient * My 401k admin has slightly higher fees (like tenths of a percent) * I'm not in a position to max my IRA in addition to making significant post-tax 401k contributions Am I right that contributing to an in-plan Roth conversion with my 401k admin is equivalent, if not marginally better, than contributing the same amount to a Roth IRA? If you have the option of an in-plan Roth conversion, why bother with a Roth IRA?