What do you mean exactly?
The topic is about the increase of USDT market cap, but you're asking about bullish market and the possibility of Bitcoin crash. 
Anyway, bullish season has been starting since the early of this year. You can see that Bitcoin has made a new ATH. I think it is very visible for everyone. Regarding the current big decrease of Bitcoin price, it is not so surprising due to many FUDs or bad news recently.
What I meant is that we are still in a bull market and those who have investments will prefer to be in Bitcoin because the possibility of its value increasing is high. However, stablecoins will gain momentum, so what will happen when the Bitcoin price starts to correct and everyone wants to buy stablecoins and sell their Bitcoin.
Your statement is clear and makes an important point. You say that even though we are in a bull market and the price of Bitcoin is likely to increase, some investors may invest in stablecoins to seek safety due to the current market volatility.
Bitcoin is highly likely to achieve a new all-time high (ATH) price amid the current bull market, but a temporary drop in Bitcoin price is also not unexpected, especially due to the impact of FUD (Fear, Uncertainty and Doubt) and bad news.
If the price of Bitcoin suddenly drops significantly and people start moving to stablecoins for safety, this could cause the market capitalization of stablecoins to increase. However, in the long run, when the value of Bitcoin starts to recover, we may see a flow of funds towards Bitcoin again, which may lead to an exit from stablecoins.
In short, the ongoing balance between Bitcoin and Stablecoin will depend on investor sentiment and market conditions. Those who believe in Bitcoin may stay during that decline, but many may temporarily switch to stablecoins so they can buy Bitcoin after the price corrects.