I don't think the solution you suggest is appropriate for the game. Removing yourself from the battle is a legitimate tactic, albeit an annoying one for the team that now has to hunt the other team down. I remember times when we were outgunned or outmatched, and had to use hit-and-run tactics throughout the entire game to remain competitive. It is one of the only ways to separate lighter mechs from an assault group...bait and run to draw them out. I also remember having this done to us plenty of times, and although it usually pissed everyone off and occasionally we lost pilots due to time issues, you had to give props to the guy that managed to elude you for the remainder of the match. Plus, maybe you'll think twice about running an assault mech after chasing around a light for an hour at 45 kph. Forcing that light mech to now come to you completely removes any advantage he has.
Seems to me that an attrition style match is pretty much what you are wanting. If you want the game skewed in favor of the stronger team, attrition pretty much handles that. I can see having one team protect a map objective, i.e. attackers vs. defenders, and any attacker that cannot take control of the objective point loses... But back on point, I think a final capture point would just mean that once a team gains the upper hand, they will hold that point until the match timer runs out. And if all maps are designed so that this capture point is so exposed that they would be subject to attack from all sides, yet the opposition would remain under cover...well that would be a boring map, and all maps would be forced to have this generic feature. And it's not like they will have a range advantage or anything...in fact a heavier group is typically going to have longer range weapons, so a lighter group would always be at a disadvantage if the heavy group decided to go camp the final cap point. A better option for what you are wanting would be to start a countdown timer after any period of inactivity, then after so much time end the match with the win going to the team with the higher attrition score.
I understand what you mean by forcing a draw...sure, it's cheesy. But strategically (for non-respawn planetary), it should remain an option simply because it is a realistic strategy (for example, chess). I suppose some leagues do not handle this situation well, and honestly I think that is a problem with the league, not the game. In my case (Lance Command), any remaining mechs (or other equipment) remaining at the end of a match are given the opportunity to retreat to a friendly area or they can drop with the next wave. A battle doesn't end until all equipment has retreated or has been destroyed. I think that is much more realistic as opposed to an all-or-nothing mindset.
In my opinion, regardless of what restraints you have placed on the game, people will find the most advantageous method of exploiting it. I don't think forcing everyone to fight within a very narrow interpretation of purpose is the answer. Let the game find its balance and let the leagues adapt.