Lotus had some nice technology in engine, and tuning. In the early 2000s, Proton wanted to use the Lotus engine technology to create a new generation of homegrown engines. The Campro engine project. Prior to that, Proton cannot produce its own engines. Nevertheless, the Campro engine project failed mainly due to incompetence. The engine was produced, but it was terrible, nothing like what it was envisioned to be. They eventually gave up Campro and went back to importing engines from Mitsubishi, Honda, etc. Proton had Lotus engineering input, and yet it still could not design a proper petrol engine in the early 2000s. They can't even reverse-engineer engine technology that they had bought! That gives you an idea of how incompetent Proton is.
Yes, having access to Proton's sales and distribution network in Malaysia is great to push Geely sales into the market. But there is one major limitation: Proton is only strong in Malaysia. In the greater SEA, Proton is neither common, nor desirable. Toyota dominates Thailand, and parts of Indochina. Wuling, and other Chinese companies are doing quite well in Indonesia. Geely would be better off just doing the sales and distribution themselves outside of Malaysia. Proton has no brand power outside of Malaysia.
On paper only. Geely is running the show behind the scenes. Because the Proton management are so clueless, they would rather let Geely run the show on their behalf. And why not? Geely gets to puppet Proton, while the Proton management get their free wages, and free credit. Proton still gets to improve under Geely's management. Its a win-win deal.