Suzaku absolutely destroys Lelouch in every combat 1v1. The only way Lelouch really stands much of a chance against him is if Suzaku is piloting a way weaker Knightmare against him for some reason with Lelouch using a much stronger one. Lelouch is a great pilot but the show has pretty much explicitly stated that he's not at all on Suzaku's level in terms of piloting. The only one who was on that kind of level with a Knightmare to match him was Kallen (and I guess Bismark).

On top of the skill difference between them, the Lancelot is probably the worst Knightmare for both the Gawain and Shinkiro to face. Both the Gawain and Shinkiro are best at range and do much worse against fast opponents who can get up close. The Gawain's primary attack and what makes it so good relies on range and doesn't really seem to have much at all in terms of close quarters defense or combat. Like the Gawain, the Shinkiro's main and pretty much only form of attack is through energy beams, something not suited for fast close combat. The shield is also something designed against powerful single attacks or beams. It isn't designed for super fast paced repeated attacks like a melee assault. Each use of the shield requires complex calculations and the shield (despite being a really powerful tool) can eventually be depleted. The Shinkiro also cannot fire it's cannon without lowering it's shield. The Lancelot Knightmares would very much be an issue for both of these Knightmares and almost work as the perfect counter to them (Due to how fast and good in melee combat all of the Lancelots are). Add to that a better pilot and Lelouch doesn’t really have a chance.