They needed equipment more. The Romanians are most know for their failure in the counter attack at Stalingrad. It has been quite a while since I read the book, but from memory, they had about one heavy anti-tank weapon per battalion, and closer to one per regiment. This is way below what a mid level German division had. Bravery and good leadership without anti-tank weapons don't stop T-34 in open country. Weapons are required. Now it is possible that even with an SS TOE, the Romanians would have performed poorly due to bad leaders, but we will never know for sure. And to be fair to the Romanian, the ratio of men to front was so low, I am not sure that the best Germans divisions would have slowed the attack for more than a few hours more than OTL. I would lean towards SS divisions delaying the Soviet attack for a couple of days more than OTL, but I can't support this assertion in detail.
And actually I believe according to Axworthy in Third Axis Fourth Ally, Romanian armored division did stall Soviet attacks at Stalingrad for a bit, but needed to be reinforced (by famous by Russian patriotic mice stopped 22nd Panzer). So better equipment (Pz III and IV instead of Pz-35 and Pz-38, more AT) could help a lot.
Sure Soviets would get through sooner or later, but with better equipment initial Romanian success could be less bloody, so morale of the troops would be even higher and they could inflict bigger losses to Soviets.
Just but size of the army Romanians should have at least 3-4 tank divisions.
I believe in 1937-1938 Romanians were trying to get license rights for Czechoslovak LT-35. Which as tank hunter served in Romanian army till the end.
Romanians did produce French Renault armored carrier UE in Malaxa factory.
In 1939 Romanians were trying to order from Czechoslovakia medium tanks. At the end the opted for order of 216 T-21 tanks. But due to German occupation of Czechoslovakia, the order was never delivered or even started. Even if T-21 with its original I believe 4.7 cm gun would be in 1941 against Soviet modern tanks under gunned, 216 of them could be huge help during initial attacks. Especially when Romanians LT-35 get pretty much decimated in early summer 1941 and were not available to support another thrust into southern Ukraine.
More modern artillery would help too.
Also, Romanians were trying to get their hand on Fw 190's BMW engine which they wanted to use in their IAR 80/81 fighter planes.