Rule 17 and the definition of proper course

PL is borderline overlapped and about 1 boat width to leeward, the exact relationship is however unimportant (bear with me) but it is clear to all that PW cannot gybe until PL does without breaking rule 15. 

They gradually approach from clear astern a Symmetrical Boat, also on Port Tack, who is running deeper to the same mark and will not need to gybe.  The Symmetrical boat is not racing PL and PW, so the Symmetrical boat does not defend but simply wishes them to get on past as soon as possible.

PW passes to windward of the Symmetrical Boat, but for reasons known only to themselves, PL establishes an overlap within 1 boat width to leeward of the Symmetrical Boat.  Who sighs with frustration and comes up to match the course that both PL and PW have been maintaining before they established the overlap.

PW sees this as a golden opportunity to break the control that PL had over them, and reacts by going very high, clearly intending to create enough space to gybe onto Starboard.

PL reacts by altering course towards PW, heading up far higher than their previously maintained course, in order to try and stop them gaining the separation they would need to execute a gybe.  A debate about proper course breaks out between PL and the now very annoyed Symmetrical boat, who points out that they are being taken higher than the course PL was sailing before they established the overlap a course that they had been sailing for some minutes previously and that matched the course of the other identical boats in sight, and a course that has resulted in both boats sailing away from the mark and struggling to keep kites flying. The Symmetrical boat never the less reacts to PL's luff and keeps clear.  

The definition of PROPER COURSE says "A course a boat would sail to finish as soon as possible in the absence of the other boats referred to in the rule using the term."

There is no doubt that without the symmetrical boat PL would have reacted to PW's manoeuvring by going with them, they were basically match racing for a place on the final meaningful leg.  (The next mark being a leeward mark followed by a very short fetch to the finish).  But without the symmetrical boat PW would not have done that.  It is also true that heading up in this way is not the course for PL to finish as soon as possible, as it is clearly away from their best VMG it's just a course that might enable them to finish in front of another boat.  

Question.  Did PL break rule 17?

[Pedant hat] Minor point, but it's "a course a boat would sail to finish as soon as possible in the absence of the other boats referred to in the rule using the term...."

So take this scenario below, and saying that 17 applies between yellow and blue. When determining yellow's proper course, we can "remove" blue and see what that does to yellow's course. But yellow's proper course is to avoid green, so even though she sails higher than before, she doesn't sail higher than her proper course, and doesn't break 17. 

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