In every team, many requirements, standards and interests pull against each other. The timeline is tight, money is short, and at the same time the goals and the expectations for quality are high. Sooner or later, the team ends up with a compromise. Everyone only sees their own area, their own deadlines and their own pressure, and from that perspective the compromise seems reasonable.
The same applies here as with company culture: you get what you tolerate. If you tolerate lower standards, your team reconciles conflicting requirements the easiest way, by lowering the requirements. Over time, these compromises add up and make your team, your products, your sales and ultimately your entire company worse, and therefore less successful.
Meeting conflicting requirements anyway is maddening. It feels like an impossible, unfair task. That's exactly why you have to get the best out of your team, and you can only do that if you're uncompromising and accept nothing less than these high standards. Uncompromising also means: anyone who works against the standards has to leave the team.
Enforcing standards doesn't require raising your voice. When a proposal falls below your standard, hand it back with one clear sentence: "This isn't at the level we need yet. The analysis of the alternatives is missing. Send me a new version by Thursday." What matters is that you do this every time. If you only do it sometimes, your team learns that the standard is negotiable.
Only you can do this, because everyone else on the team has good reasons for the compromise: their own deadline, the tight budget, harmony with colleagues. You're the only one who sees the whole picture, carries the final responsibility and ultimately has to live with the consequences of every compromise. And only you have the authority to say no to every area at once and to follow through with consequences. Your team takes its cue from what you accept. That's why only you can set this standard and hold it.