FALSE.
Incumbents win re-elections in overwhelming numbers.
TRUE.
It is far harder to dislodge an incumbent democrat compared to defeating a RINO in next primary.
The RINO, being by then an incumbent, see your second point.
A RINO can be persuaded to vote conservative at least on some issues. Democrats of today will vote liberal every time.
FALSE. A liberal is a liberal is a liberal.
If you read my post again, I allude to defeating the RINO in the NEXT PRIMARY if he/she can not be persuaded to vote more conservative. The incumbent democrat will be difficult to defeat in the next GENERAL election, as an incumbent.
General versus Primary are completely different situations. You should try to understand the difference.