In 95% of circumstances yes breaking into two one ways will cost you more than the savings on YQ for a UK-originating one way upgrade on the return.

IF you are flying a regular pattern of US-UK flights, I would advise you to consider basically structuring your tickets as UK originating. I did this nearly a decade ago when I went to and from London every three weeks to see my now wife. I was an AA flier then so this wasn't about YQ on BA. However, generally speaking Y and W fares from the UK-US are lower than the reverse. In some cases, its less than 50%. For example, I've seen LHR-IAH in Y for ~500 GBP when the reverse was $1600 on the same dates. While the change fee universe is changing due to COVID, etc. - change fees are generally lower on UK originating tickets.

If you are flying on BA and looking to upgrade, my guess is over a year you would spend barely more than 50% if structuring tickets as UK originating vs US originating.

The downside of course is needing to (i) get to the UK once to start the process and (ii) having a general idea as to when the next trip is (though with decreasing change fees, COVID waivers, etc. - that may be a surmountable hurdle).