Your decision to apply under the family/partner route is correct and the advisor is wrong. If you qualify to apply under the 10-year partner/family route, you also have the option to apply under the long residence rules using form SET(LR). The advisor therefore is wrong to suggest that it is one or the other route.
FYI
You seem to have incorrectly interpreted the note on the form SET(LR). That note simply says to avoid using form SET(LR) if you intend to apply for ILR under the family/partner route rules (i.e. the 10-year FAMILY route) as you should use a different form ('adult settlement'). However, it does NOT talk about your current visa or tell you that you cannot use SET(LR) if they happen to be on the family route. Under the long residence, your current visa route is irrelevant. In your case, you had the option to apply under both routes.
The only difference is that the rules are different for each route. My suggestion is that if someone qualifies under the family route, they better stick to that as you did. The long residence has gone through several changes recently, so some people
may no longer qualify.
See:
Lawful and continuous residence changes to Long Residence route from 11 April 2024
Advice is given based on my personal research and experience only. Do NOT contact me via private message for immigration advice